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Technische Universität München Lehrstuhl für Anorganische Chemie Ionic Catalysts for the Cycloaddition of Carbon Dioxide with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von der Fakultät für Chemie der Technischen Universität München zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigten Dissertation. Vorsitzende(r): Univ.-Prof. Dr. F. E. Kühn Prüfer der Dissertation: 1. Univ.-Prof. Dr. Dr. h.c. mult. W. A. Herrmann 2. Prof. Dr. Dr. h.c. J. Mink, Universität Budapest/Ungarn Die Dissertation wurde am 29.06.2015 bei der Technischen Universität München eingereicht und durch die Fakultät für Chemie am 23.07.2015 angenommen.

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Page 1: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

Technische Universität München

Lehrstuhl für Anorganische Chemie

Ionic Catalysts for the Cycloaddition of Carbon Dioxide

with Epoxides and the Oxidation of Olefins

Michael Edmund Wilhelm

Vollständiger Abdruck der von der Fakultät für Chemie der Technischen Universität

München zur Erlangung des akademischen Grades eines

Doktors der Naturwissenschaften (Dr. rer. nat.)

genehmigten Dissertation.

Vorsitzende(r): Univ.-Prof. Dr. F. E. Kühn

Prüfer der Dissertation:

1. Univ.-Prof. Dr. Dr. h.c. mult. W. A. Herrmann

2. Prof. Dr. Dr. h.c. J. Mink, Universität Budapest/Ungarn

Die Dissertation wurde am 29.06.2015 bei der Technischen Universität München

eingereicht und durch die Fakultät für Chemie am 23.07.2015 angenommen.

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Page 3: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

Most people say that it is the intellect which makes a great scientist.

They are wrong: it is character.

Albert Einstein

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Die vorliegende Arbeit wurde am Anorganisch-Chemischen Institut der Technischen

Universität München in der Zeit von Juli 2012 bis Juli 2015 angefertigt.

Besonders danken möchte ich meinem verehrten Lehrer und Doktorvater

Herrn Professor Dr. Dr. h.c. mult. Wolfgang A. Herrmann

für die Aufnahme in den Arbeitskreis, für die uneingeschränkten Forschungsmöglich-

keiten, für die verschiedenen Themenstellungen und für das entgegengebrachte Ver-

trauen in meine Arbeit.

Weiterhin gilt mein besonderer Dank

Herrn Professor Dr. Fritz E. Kühn

für die Erschaffung eines großzügigen und positiven Arbeitsumfelds, für das große

Interesse an meiner Arbeit und für die Möglichkeit an wunderbaren Nebenprojekten

teilzunehmen. All dies, sowie die Korrekturen von zahlreichen Manuskripten, haben

maßgeblich zum Gelingen dieser Arbeit beigetragen.

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Acknowledgments

An dieser Stelle möchte ich mich bei der Vielzahl an Personen bedanken, die mich

fachlich und persönlich während der Dissertation unterstützt haben und so einen ent-

scheidenden Beitrag für das erfolgreiche Gelingen dieser Arbeit geleistet haben.

Mein besonderer Dank gilt dabei:

Dr. Mirza Cokoja für die freundschaftliche und tatkräftige Betreuung meiner Arbeit,

die zahlreichen Korrekturen von Publikationen und häufigen wissenschaftlichen und

nicht-wissenschaftlichen Gesprächen in Verbindung mit großzügigen Kaffeerunden.

Dr. Alexander Pöthig für die freundschaftliche Unterstützung, die Bestimmung eini-

ger Kristallstrukturen und amüsante Unterhaltungen.

Dr. Gabriele Raudaschl-Sieber für nette fachliche und persönliche Gespräche, die

schöne Arbeitsatmosphäre während der Klausurkorrekturen und Praktika, sowie für

leckere und üppige Mittagessen in der Innenstadt und in Garching.

Dr. Markus Drees für zahlreiche DFT Rechnungen, die Klärung organisatorischer

Fragen und witzige Fußball- und Fachdiskussionen.

Professor Dr. János Mink, Dr. Jason Love, Dr. Valerio D’Elia und Prof. Dr. An-

dreas Jess, Dr. Wolfgang Korth sowie Johannes Schäffer für schöne gemeinsa-

me Projekte, die professionelle, angenehme Zusammenarbeit und dem gesamtem

Team aus Bayreuth für eine tolle gemeinsame Zeit auf Konferenzen.

Dr. Michael Anthofer für die großartige Unterstützung, Zusammenarbeit und

Freundschaft während des Studiums, der Promotion und darüber hinaus, sowie für

die großartige Zeit während Konferenzen und dem Verzehr von Gutmännern und

anderen Köstlichkeiten.

Dominik Höhne für den überragenden fußballerischen Wettbewerb mit vielen hitzi-

gen Diskussionen und Momenten, sowie die erheiternde Atmosphäre im Labor und

anderen Aktivitäten.

Robert Reich für eine erfolgreiche Zusammenarbeit, seine künstlerische Kreativität

bei der Erstellung von Bildern und unzählige sinnlose bzw. sinnvolle Gespräche.

Marlene Kaposi für die erfolgreiche und angenehme Zusammenarbeit, viele lustige

fachliche und persönliche Gespräche bei Kaffee oder Mittagessen und die schöne

Zeit auf Konferenzen.

Meinen Laborkolleginnen Xumin Cai, Eva Hahn und Sara Abassi für die angeneh-

me Arbeitsatmosphäre, erheiternde Fachgespräche und Diskussionen über interkul-

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turelle Verhaltensweisen und Kochkünste sowie das ständige Update der Laboraus-

stattung.

Meinen guten alten und neuen Kollegen Iulius Markovits, Christian Münchmeyer,

Korbinian Riener, Ruth Haas, Dr. Lilian Graser, Dr. Daniel Betz, Dr. Andreas

Raba, Dr. Dominik Jantke und Dr. Reentje Harms für Ihre Unterstützung, sowie die

schöne Zeit an der Universität und bei allen anderen Aktivitäten.

Allen weiteren Arbeitskollegen aus den Arbeitskreisen Herrmann und Kühn danke ich

für den tollen Teamzusammenhalt, ihre Hilfsbereitschaft und die lockere Atmosphäre.

Meinen Forschungspraktikanten, Bacheloranden und Christine Hutterer für die tat-

kräftige Mitarbeit im Labor und die guten Auswertungen.

Den allseits freundlichen Sekretärinnen Irmgard Grötsch, Roswitha Kaufmann,

Renate Schuhbauer-Gerl und Ulla Hifinger für ihre tatkräftige und kompetente Un-

terstützung in kleinen und großen organisatorischen Fragen.

Jürgen Kudermann, Maria Weindl, Rodica Dumitrescu, Ulrike Ammari, Petra

Ankenbauer, Bircan Dilki und Martin Schellerer für die Unterstützung bei NMR

Experimenten, die Charakterisierung zahlreicher Verbindungen sowie zügige Liefe-

rungen und Versendungen von Chemikalien.

Außerdem möchte ich mich bei meinen Eltern und meinem Bruder von ganzem Her-

zen bedanken. Sie haben zu jedem Zeitpunkt meines Lebens alles in ihrer Macht

stehende getan, um mich zu unterstützen.

Schließlich gilt mein ganz besonderer Dank meiner Freundin Corinna, die mich durch

ihre liebevolle Art und den Glauben an meine Fähigkeiten immer unterstützt und ein

großer Rückhalt für mich ist auf den ich mich immer verlassen kann.

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Deutsches Abstract

Imidazoliumsalze werden als Katalysatoren und Lösemittel in vielseitigen Bereichen

eingesetzt. In dieser Arbeit liegt das Hauptaugenmerk auf dem Zusammenhang der

Struktur des Imidazoliumkations mit der Reaktivität des nukleophilen Anions als kata-

lytisch aktive Spezies. Durch Modifizierung des Imidazoliumkerns mit organischen

Substituenten werden die elektrostatische Wechselwirkung der Ionen und damit auch

die Eigenschaften des Anions stark beeinflusst. Die wichtigsten Faktoren in Bezug

auf die Reaktivität des Anions sind dabei sowohl die sterische Zugänglichkeit des C2

Protons, als auch dessen Azidität. Ferner hängt das Löslichkeitsverhalten von Imida-

zoliumsalzen vom Substitutionsmuster des Kations ab, was sich ebenfalls auf die

Aktivität auswirkt.

Die Untersuchung der katalytischen Cycloaddition von Epoxiden mit Kohlenstoffdi-

oxid stellt einen Großteil dieser Arbeit dar. Dabei wurden die Auswirkungen der

Struktur des Kations auf die Aktivität von Imidazoliumhalogeniden als Katalysatoren

analysiert. Die gewonnenen Erkenntnisse ermöglichen die Optimierung des Substitu-

tionsmusters, sodass eine stärkere Aktivierung des Epoxids und eine höhere katalyti-

sche Aktivität erreicht werden. Des Weiteren wurden die Auswirkungen verschiede-

ner Imidazoliumsubstituenten in einem binären Katalysatorsystem in Kombination mit

Niob(V)-chlorid als Lewis Säure untersucht. Die sterischen und elektronischen Ei-

genschaften der Imidazoliumsalze sowie deren Löslichkeit konnten als entscheiden-

de Aspekte für die Aktivität ermittelt werden. Durch Kombination eines Polyols, wel-

ches zur Aktivierung des Epoxids dient, mit einem Halogenid als Nukleophil wurde

außerdem eine organokatalytische Alternative zu Lewis-aziden Metallen geschaffen.

Darüber hinaus wurden Imidazoliumsalze für die Epoxidation von Olefinen mit wäss-

rigem Wasserstoffperoxid benutzt. Durch säurefunktionalisierte Imidazoliumkationen

konnten Polyoxomolybdate mit guter katalytischer Aktivität in situ aus günstigen und

leicht verfügbaren Vorstufen erzeugt werden, wodurch die Reaktionsführung verein-

facht wurde. Zusätzlich wurde erstmals gezeigt, dass Imidazoliumperrhenate als Ka-

talysatoren für die Epoxidation von Olefinen fungieren können. Durch Strukturopti-

mierung des Kations konnten ein geringes Ausmaß an Ionenpaarung, und damit eine

effiziente Aktivierung von H2O2, sowie eine erhöhte Olefinlöslichkeit in der wässrigen

Phase ermöglicht werden. Somit wurde ein aktives, einfaches und wiederverwendba-

res Katalysatorsystem für die zweiphasige Epoxidation von Olefinen erhalten.

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English Abstract

Imidazolium salts are versatile compounds, being used as catalysts and solvents for

a wide range of applications. The primary focus of this thesis is placed on the correla-

tion between the imidazolium structure and the reactivity of the nucleophilic anion as

catalytically active species. Upon modification of the imidazolium pattern with varying

organic residues, the electrostatic interaction between the ions and thus the proper-

ties of the anion are significantly influenced. In particular, the steric accessibility and

the acidity of the C2 proton are key factors affecting the anion reactivity. Furthermore,

the solubility behavior of imidazolium salts depends on the cation structure to a large

extent, which results in strong effects on the catalytic activity.

The major part of this work deals with the catalytic cycloaddition of epoxides with

carbon dioxide towards cyclic carbonates. For this purpose, imidazolium halides were

applied as organocatalysts and the impact of the cation structure on the activity was

analyzed. Therefore, the optimization of the imidazolium ring substitution pattern was

enabled, with respect to reinforced activation of the epoxide through hydrogen bond-

ing. As a result, enhanced catalytic activity was achieved. Aside from imidazolium

salts as single catalysts, the effects of various cation residues were investigated in

combinations with niobium(V) chloride as Lewis acid. The changes in the steric and

electronic properties and epoxide solubility were determined as the most important

aspects influencing the activity of the binary catalyst system. Further, a binary mix-

ture consisting of a polyol, as epoxide activator, and halides, as nucleophiles, was

found to be a promising organocatalytic alternative to systems based on Lewis acidic

metals.

Imidazolium salts were also employed as catalysts for the epoxidation of olefins with

aqueous hydrogen peroxide. It was shown that catalytically active polyoxomolybdates

can be generated in situ with carboxy-functionalized imidazolium salts. Consequently,

the reaction procedure was facilitated and a good catalytic performance was ob-

tained, whereby cost-efficient and readily available precursors were used. Additional-

ly, it was demonstrated for the first time that imidazolium perrhenates are able to act

as epoxidation catalysts. By optimizing the cation structure, a low degree of ion pair-

ing, and hence strong H2O2 activation, as well as enhanced olefin solubility in the

aqueous H2O2 phase were enabled. Finally, an active, simple and reusable catalyst

system for the biphasic epoxidation of olefins with H2O2 was achieved.

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Abbreviations

AER anion exchange resin

APT azaphosphatranes

BMim 1-butyl-3-methylimidazolium

CO2 carbon dioxide

DBU 1,8-diazabicyclo[5.4.0]undec-7-ene

DFT density functional theory

FTIR fourier transform infrared spectroscopy

HB hydrogen-bond

HFIP 1,1,1,3,3,3-hexafluroisopropanol

HPPO hydrogen peroxide propylene oxide

IL ionic liquid

LCA life-cycle-assessment

NMR nuclear magnetic resonance

PC propylene carbonate

PEG polyethylene glycol

PETT pentaerythritol

PO propylene oxide

POM polyoxometalate

PS polystyrene

PTC phase transfer catalysis

SC styrene carbonate

SO styrene oxide

TBAB tetrabutylammonium bromide

TBAI tetrabutylammonium iodide

TBD triazabicyclo[4.4.0]dec-5-ene

TR transfer reagent

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Table of Contents

Acknowledgments _________________________________________________________________ vi

Deutsches Abstract _______________________________________________________________ viii

English Abstract ___________________________________________________________________ ix

Abbreviations ______________________________________________________________________x

1 Introduction ___________________________________________________ 1

1.1 Organocatalytic Cyclic Carbonate Synthesis from Epoxides and CO2 ______ 1

1.1.1 CO2 as Sustainable Chemical Building Block _________________________________ 1

1.1.2 Ionic Organocatalysts for the Cycloaddition of CO2 to Epoxides ___________________ 3

1.1.3 Synergistic Binary Systems ______________________________________________ 11

1.2 Epoxidation of Olefins ____________________________________________ 13

1.2.1 Olefin Epoxidation in the Chemical Industry _________________________________ 13

1.2.2 Multi-Phasic Olefin Epoxidation Using Ionic Compounds _______________________ 15

1.2.3 Activation of H2O2 by Hydrogen Bonding ___________________________________ 19

2 Objective of the Thesis _________________________________________ 23

3 Results and Discussion ________________________________________ 24

3.1 Publication Summaries ___________________________________________ 24

3.1.1 Cycloaddition of CO2 and Epoxides Catalyzed by Imidazolium Bromides under Mild

Conditions: Influence of the Cation on Catalyst Activity _______________________________ 24

3.1.2 Hydroxy-Functionalized Imidazolium Bromides as Catalysts for the Cycloaddition of CO2

and Epoxides to Cyclic Carbonates ______________________________________________ 26

3.1.3 Niobium(V)chloride and Imidazolium Bromides as Efficient Dual Catalyst Systems for the

Cycloaddition of Carbon Dioxide and Propylene Oxide _______________________________ 28

3.1.4 Cycloaddition of Carbon Dioxide and Epoxides Using Pentaerythritol and Halides as

Dual Catalyst System _________________________________________________________ 30

3.1.5 Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in situ in Ionic Liquids32

3.2 Epoxidation of Olefins Using Ionic Liquids as Phase Transfer Catalysts __ 34

3.2.1 Results and Discussion _________________________________________________ 34

3.2.2 Experimental Details ___________________________________________________ 38

3.2.3 Synthesis and Characterization of the Catalysts ______________________________ 39

4 Summary and Outlook _________________________________________ 45

5 Bibliographic Data of Complete Publications _______________________ 52

6 Reprint Permissions ___________________________________________ 55

6.1 RSC Publications ________________________________________________ 55

6.2 De Gruyter Publication ____________________________________________ 55

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6.3 Wiley Publications _______________________________________________ 55

7 References ___________________________________________________ 62

8 Curriculum Vitae and Publications _______________________________ 69

8.1 Curriculum Vitae _________________________________________________ 69

8.2 Journal and Book Contributions ____________________________________ 70

8.3 Talk and Poster Presentations _____________________________________ 71

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1. Introduction

1

1 Introduction

1.1 Organocatalytic Cyclic Carbonate Synthesis from Epoxides and CO2 1.1.1 CO2 as Sustainable Chemical Building Block

Chemistry strongly depends on the availability of fossil fuels, as they are used as raw

materials for the preparation of the majority of available products.[1] Additionally,

many industrial processes are energy intensive, so that approximately 10 % of the

global energy, which is mainly produced from fossil fuels, is consumed by the chemi-

cal industry.[2] In order to alleviate the effects of growing fossil fuel depletion on the

chemical industry, renewable carbon feedstocks represent a promising opportunity.[3]

In addition to ligno-cellulosic biomass,[4] or oils and fats,[5] the usage of carbon diox-

ide, as one of the most abundant renewable carbon sources, is of particular high in-

terest.[6] Besides the omnipresence of CO2, to which the human emission amounts to

more than 30 Gt/y, the greenhouse gas is non-toxic and cheap and therefore a suita-

ble candidate as C1-feedstock in industry.[7] The major drawback of CO2 as a building

block is its high stability and low reactivity originating from the carbon atom in the

most oxidized state.[8] Consequently, a vast amount of energy needs to be applied,

which negatively affects the costs and environmental benignity.[9] Therefore, less

than 0.5 % of the anthropogenic CO2 emissions are used as reactant in industry

(appr. 110 Mt/y), whereby four major compound classes are produced so far

(Scheme 1.1).[8, 10]

Scheme 1.1: Industrial processes involving CO2 as chemical building block.[8]

To increase the utilization of CO2 as a building block, catalysis research is a crucial

factor. It is devoted to developing highly efficient processes, leading to lower energy

input.[11] One particular example for the catalytic chemical fixation of CO2 represents

its addition to epoxides as highly reactive starting materials. As shown in

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1. Introduction

2

Scheme 1.1, the prospective development of the scale for cyclic organic carbonate

production (upper right) is expected to increase significantly.[8] The corresponding

cycloaddition of CO2 to epoxides represents a 100 % atom economical reaction,

which is highly desirable for industry.[12] Further, highly toxic phosgene (route b,

Scheme 1.2), is eliminated using this approach (route c, Scheme 1.2).[13] Regarding

the carbon footprint, life-cycle-assessment analysis (LCA) also shows that the cou-

pling of CO2 with ethylene oxide is the most desirable route towards ethylene car-

bonate as model product.[14]

Scheme 1.2: Different routes towards ethylene carbonate with respective mass ratio of emitted CO2/

product (determined via LCA).[14]

Cyclic organic carbonates, of which propylene carbonate (PC) is the most prominent

example, can be used as high boiling polar aprotic solvents with low toxicity or as

electrolytes in lithium batteries.[15] Additionally, they can be applied as versatile feed-

stock for the manufacturing of polymers,[16] linear organic carbonates[17] or fine chem-

icals.[18] Taking these facts into account, it can be stated that this reaction has great

potential for the sustainable chemical fixation of CO2.

Unfortunately, harsh reaction conditions often have to be applied to convert the high-

ly stable CO2 to the corresponding cyclic carbonates.[19] Thus, a multitude of catalyst

systems, usually consisting of a combination of Lewis acids and nucleophiles, have

been developed to optimize temperature, pressure and reaction time. Among several,

Al,[20] Co,[21] Cr[22] and Zn[23] complexes, metal halide salts like ZnBr2[24] or (NbCl5)2,

[25]

as well as metal oxides, e.g. MgO[26], can be applied as Lewis acids. Onium, respec-

tively imidazolium halide salts, or nucleophilic N-donor bases are often used as nu-

cleophilic co-catalyst.[13] The organocatalytic valorization of CO2 with epoxides consti-

tutes an alternative approach with vast research potential, particularly for the sustain-

ability of the process. Generally, metal-free catalysts often benefit from being air- and

moisture stable, allowing for an easy and cheap preparation, as well as a simple and

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1. Introduction

3

safe handling.[27] A large part of organic compounds is comparably non-toxic and

readily available from renewable carbon sources too.[28] Therefore, organocatalysis

can not only substantially improve the costs and the development time of processes,

but also the required energy input.[29] Further, the amount of chemical wastes can

possibly be reduced and the experimental procedures can be simplified. Thus, the

carbon footprint and sustainability of a variety of operations could be optimized, in-

cluding the coupling reaction of CO2 with epoxides to cyclic carbonates. This would

offer the opportunity to use CO2 as a reactant in an environmentally benign manner.

However, this is only applicable if the demanding reaction conditions (> 120 °C,

> 20 bar CO2), under which these systems usually operate, can be enhanced signifi-

cantly.

1.1.2 Ionic Organocatalysts for the Cycloaddition of CO2 to Epoxides

The first report regarding metal-free conversion of epoxides with CO2 to cyclic car-

bonates was published by Nishikubo et al. in 1993.[30] Nearly a decade later, Calo et

al. were able to transform styrene oxide (SO) to styrene carbonate (SC) in 83 % yield

(120 °C, 4 h, 1 bar CO2). A mixture of molten tetrabutylammonium bromide (TBAB)

and iodide (TBAI) hereby served as solvent and catalyst.[31] Moreover, the reaction

mechanism for the organocatalytic cycloaddition of epoxides to CO2 was initially pos-

tulated (Scheme 1.3, (a)). In the first step the epoxide ring is opened by nucleophilic

attack of the halide anion at the sterically less hindered carbon atom. The resulting

oxy-anion species attacks the electrophilic carbon atom of CO2, forming an open-

chain carbonate species. After intramolecular nucleophilic attack and elimination of

the halide anion (‘Back-biting’), the cyclic carbonate product is finally obtained. Fur-

ther investigations by means of density functional theory (DFT) studies, combined

with experiments, confirmed the postulated mechanism.[32] Also the cation was found

to influence the catalytic activity of ammonium halides, as the degree of ion pairing to

the anion affects its nucleophilicity. Thus, TBAB shows considerably higher catalytic

activity than the methyl analog arising from the sterically more demanding alkyl

chains.[33] The next step towards more active organocatalysts involves the introduc-

tion of tailored cations, being capable of acting as a synergistic structural component

during the catalytic cycle. Therefore, OH-functionalized ammonium compounds were

applied and found to be more efficient because of their hydrogen-bond (HB) donor

ability.[34] Sun et al. were able to show that PC yield increases from 74 to 96 % by

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1. Introduction

4

substituting TBAB with its corresponding hydroxyethyl analog (Figure 1.1, (a),

125 °C, 20 bar CO2, 1 h, 1.6 mol %). Through coordination to the epoxide via HB, the

C-O bond is polarized and the nucleophilic attack of the anion is facilitated, resulting

in higher catalytic activity (Scheme 1.3, (b)).[34] More recent investigations revealed

that hydroxyethyl modified TBAI catalyzes the formation of PC at considerably milder

reaction conditions (45 °C, 10 bar CO2, 18 h, 5.0 mol %).[35] This demonstrates the

great potential of this class of catalysts. Additionally, betaine,[36] choline,[37] as well as

amino acid based ammonium salts (Figure 1.1, (b))[38] are reported as HB donor sub-

stituted catalysts for cyclic carbonate synthesis. However, their activity only slightly

deviates in comparison to conventional hydroxyalkyl ammonium halides.

Scheme 1.3: Proposed mechanisms for the cycloaddition reaction of CO2 with epoxides using (a) TBAB

[31] or (b) hydroxy functionalized ionic compounds

[34] as catalysts.

The immobilization of molecular catalysts on solid and insoluble carriers is a common

possibility to enable easy catalyst recycling through e.g. filtration. For ammonium hal-

ide catalysts, a great variety of supporting materials have been applied: polymers like

polystyrene (PS)[39] or polyethylene glycols (PEG),[40] biopolymers, e.g. cellulose[41]

and chitosan[42], as well as different types of silica[33] are reported in literature. As de-

scribed for the homogeneous case, also immobilized OH-modified ammonium hal-

ides (Figure 1.1, (c)) lead to higher activities compared to unfunctionalized

analogs.[39b] Supporting materials bearing OH groups were also shown to have a

comparable effect. Thus, silica[33] as well as biopolymers[41] (Figure 1.1, (d)) as carri-

ers lead to a similar increase in catalytic activity.

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1. Introduction

5

Figure 1.1: HB donor functionalized ammonium halide catalysts for cyclic carbonate synthesis.

In addition to ammonium halides based on conventional alkylamines, the protonation

or quarternization of nitrogen superbases results in alternative catalysts. Therefore,

guanidinium,[43] pyridinium or pyrrolidinium[44] and amidinium[45] based derivatives

have been synthesized. He et al. investigated a series of Lewis basic ionic catalysts

and found the highest activity for protonated 1,8-diazabicyclo[5.4.0]undec-7-ene

(DBU). The resulting [HDBU]Cl is supposed to stabilize the intermediates to a greater

extent, leading to a more efficient reaction.[46] More recent studies by Tassaing et al.

on the basis of protonated 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) have demon-

strated that the HB properties of these catalysts are crucial. Hence, synergistic ef-

fects and higher activities are observed applying [HTBD]Br in comparison to TBAB.[47]

In addition to their initial studies regarding ammonium halides, Nishikubo et al. have

also shown that phosphonium halides can be used as metal-free catalysts for the

cycloaddition of CO2 to epoxides.[30] Generally, phosphonium halides show very simi-

lar catalytic activities compared to their ammonium counterparts. Furthermore, the

introduction of HB donor functional groups at the cation likewise enhances the cata-

lytic activity. By modification of PPH3 with varying bromoethyl species, Lian et al. in-

vestigated the influence of HB donor groups on the catalytic activity.[48] The tailored

catalysts clearly outperformed the compounds without functionalization. Moreover,

the respective carboxy substituted compound gave slightly higher yields than the

amine or hydroxy analog, deriving from the higher polarization capability.[48] Werner

et al. further showed that hydroxyethyl modified P(n-Bu)3, bearing iodide as nucleo-

philic counteranion (Figure 1.2, (a)), catalyzes the formation of PC under relatively

mild reaction conditions (90 °C, 10 bar CO2, 3 h, 2.0 mol %).[49] As a novel cation

structure of phosphonium based catalysts, Jain et al. synthesized a cyclotriphos-

phazene core carrying three molecules of [PPh3]Cl. The multiple ion-pair motifs in-

duce enhanced catalytic activity compared to conventional [PPh3]Cl.[50] Martinez and

Dufaud et al. recently introduced azaphosphatranes (APT, Figure 1.2, (b)) as ionic

organocatalysts with another structural motif. The proton of the N-P-H core is sup-

posed to activate the epoxide via HB, while a hydrolysis sensitive carbamate species

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6

forms through CO2 insertion in the next step. By introduction of sterically demanding

amine substituents, the degradation of this species is hindered, resulting in higher

catalytic activity and stability.[51] Designing molecular cavities around the P-H site can

further stabilize the carbamate species because of their encapsulation in the gener-

ated cage. By creating a highly accessible HB center, the optimized hemicryptophane

compound gave constant activity over 96 h and was applicable under relatively mild

conditions (100 °C, 1 bar CO2, 24 h, 1.0 mol %).[52]

As described above regarding ammonium halides, the immobilization of phosphoni-

um compounds is a feasible strategy to obtain heterogeneous catalysts for the cy-

cloaddition of CO2 to epoxides. Therefore, PS,[30, 53] PEG,[54] cross-linked polymeric

nanoparticles[55] as well as silica materials[56] have been reported as carrier materials

in literature. By using silica as support for P(n-Bu)3 iodide (Figure 1.2, (c)), Sakakura

et al. achieved an activating effect deriving from the silanol HB donor groups on the

surface. This leads to significantly enhanced catalytic activity compared to the mo-

lecular compound. To demonstrate the long-time stability, the immobilized catalyst

was applied under continuous flow conditions in a fixed-bed reactor, thereby convert-

ing > 80 % PO for more than 1000 h.[57] By coupling of P(n-Bu)3 chloride to a fluorous

copolymer (Figure 1.2, (d)), the same group was able to synthesize a compound,

which combines the merits of homogeneous and heterogeneous catalysis. Under the

applied supercritical CO2 conditions (180 °C, 80 bar CO2), the catalyst readily dis-

solves, while upon venting CO2 it precipitates out of the reaction mixture and can be

separated by simple filtration.[58]

Figure 1.2: Phosphonium based halide catalysts for cyclic carbonate synthesis.

Imidazolium based systems constitute another widespread catalyst class with respect

to metal-free mediated cycloaddition of CO2 to epoxides. As their properties are

strongly influenced by the easily tunable modification sites of the imidazolium cation

structure (Figure 1.3), they can be adjusted towards the desired application. Thus, for

example the solubility and the HB properties can be tailored through the choice of the

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7

substitution pattern.[59] As expected, increasing alkyl chain length of the substituents

leads to enhanced lipophilicity.[60] This also accounts for blocking the acidic C2 posi-

tion with an alkyl group, whereby the HB strength decreases simultaneously.[60-61]

Figure 1.3: Modification sites of the imidazolium moiety for tailoring of the properties towards the de-sired application.

In the initial report dealing with imidazolium based organocatalysts for cycloaddition

of CO2 with epoxides, Peng and Deng introduced 1-butyl-3-methylimidazolium

[BMIm] Cl-, [PF6]- and [BF4]

- salts as first examples. A quantitative yield of PC was

obtained applying [BMIm][BF4], however at relatively harsh reaction conditions

(110 °C, 25 bar CO2, 6 h, 2.5 mol %).[62] First attempts concerning the influence of

the cation on the catalytic performance were carried out under supercritical condi-

tions. Upon increasing the alkyl chain length at the wingtip position, CO2 as well as

PO solubility increase and higher yields are observed.[63] Further, Park et al. have

shown that sterically more demanding imidazolium cations lead to a lower degree of

ion pairing and thus higher nucleophilicity of the anion. Also Cl- gave a significantly

better yield than [PF6]- and [BF4]

-, deriving from its higher nucleophilicity as decisive

factor for the ring-opening of the epoxide.[64] As aforementioned, HB donor groups at

the cations of ammonium and phosphonium halides lead to an enhanced catalytic

activity. The epoxide is activated in the first step, so that the following nucleophilic

ring-opening is accelerated. This was also found for –OH and –COOH modified imid-

azolium halide catalysts. Thus, 2-hydroxyethyl wingtip substituted 3-methyl-

imidazolium bromide gave 99 % yield of PC compared to 83 % applying the non-

functionalized analog.[34] The modification of the acidic C2 proton with a hydroxyme-

thyl group represents another route towards HB donor carrying imidazolium catalysts.

However, the catalytic activity was very similar compared to the wingtip functionalized

compounds.[65] As the Brønsted acidity and HB donor strength of carboxy groups are

higher than for hydroxy groups, their synergistic effect is expected to be more pro-

nounced.[66] Consequently, a higher catalytic activity should be observed, which was

confirmed by several studies.[67] By introducing a –COOH functional group at both

wingtips of the imidazolium cation, Zhang et al. could even further improve the cata-

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1. Introduction

8

lytic activity (Figure 1.4, (a)). It is assumed that the second carboxy unit has a rein-

forcing effect on the epoxide ring-opening, leading to higher conversions.[67b] Wu et

al. could also show that the catalytic activity strongly depends on the Brønsted acidity

of the species used for functionalizing the imidazolium motif. A considerably de-

creased yield compared to a carboxy group is observed for a catalyst bearing a sul-

fonic acid motif. The HB between the epoxide and the very acidic sulfonic group is

presumably too strong, so that CO2 insertion is hindered, resulting in a lower catalytic

activity.[68] DFT studies from Zhang et al. revealed that the acidic proton in C2 posi-

tion of the imidazolium cation is also capable to synergistically interact during the

mechanism through HB. Thus, the reaction mechanism is modified and the energy

barrier is reduced significantly.[69] As the acidity of the C2 proton and therefore the

HB donor strength is influenced by the substituents at the imidazolium ring, tailoring

of the structure enables an improvement of the catalytic activity. To investigate the

influence of the substituents in R1, R2 and R3 position, a series of ten imidazolium

bromides was synthesized and used as catalysts for the cycloaddition of PO to

CO2.[70] By substituting the acidic C2 position with alkyl residues, the PC yield de-

clines. This is ascribed to the blocking of the most dominant HB donor site, leading to

an essentially lower degree of epoxide activation. FTIR investigations underpin that

although the whole imidazolium ring interacts with the epoxide, the most pronounced

interaction derives from HB of the C2 proton. By modification of one of the wingtips

with an electron withdrawing fluorinated benzyl group, the acidity and thus also the

HB interaction and the catalytic activity were enhanced. For the further systematic

structural optimization, a n-octyl alkyl side chain was introduced at the second wingtip

site, leading to an enhanced solubility in the reaction medium. The obtained task

specific ionic liquid catalyst (Figure 1.4, (b)) was able to catalyze the formation of PC

in 91 % yield at very mild reaction conditions (70 °C, 4 bar CO2, 22 h, 10.0 mol %).[70]

Comparable investigations were performed by Dupont et al. through comparison of

the catalytic performance of 21 structurally varied imidazolium based ionic liquids.[71]

The HB donor activation of the epoxide by the imidazolium catalyst was found to be

crucial for its nucleophilic ring-opening as the rate-determining step. Moreover, the

nucleophilicity and leaving group ability of the anion are major factors towards high

catalytic activity.[71] More recently, hydroxy modified bis-imidazolium bromides were

introduced as catalysts for the cycloaddition of CO2 with epoxides.[72] The three HB

donor groups in spatial proximity lead to a more efficient epoxide activation and stabi-

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1. Introduction

9

lization of transition states and intermediates. This was corroborated by DFT calcula-

tions, thereby confirming previous studies regarding pyrogallol as component in bina-

ry catalyst systems.[73] Through substitution of the second wingtip of the bisimidazoli-

um bromide with a long alkyl chain (Figure 1.4, (c)), the solubility behavior is im-

proved, which leads to an optimized catalytic activity.[72]

Figure 1.4: Tailored imidazolium bromide catalysts for the synthesis of cyclic carbonates through cy-cloaddition of CO2 to epoxides.

The specifications of the imidazolium moiety to reach high catalytic activity change

drastically by addition of (NbCl5)2 as Lewis acidic cocatalyst.[25b] The coordination

strength of the metal center to the epoxide is significantly stronger than the HB inter-

action of the imidazolium C2 proton. Hence, the nucleophilicity of the anion and thus

the ion pairing is the decisive factor and alkyl substitution in C2 position leads to en-

hanced catalytic performance. The imidazolium solubility also influences the catalytic

activity, so that long aliphatic wingtips improved reactivity compared to short alkyl

chains or aromatic substituents.[25b]

The easy modifiability of the imidazolium moiety opens the possibility for further tun-

ing of their organocatalytic properties to enable even milder reaction conditions and

minimized carbon footprint. Especially the modification of the backbone with func-

tional groups capable of activating the epoxide through HB could lead to enhanced

catalytic activity. In addition, the ion pairing to the anion could be weakened, leading

to higher nucleophilicity and better catalytic performance. The variation of the bridg-

ing group between bisimidazolium salts could additionally result in more efficient

catalysts.

To facilitate the recycling procedure, imidazolium based catalysts were also immobi-

lized on a great variety of carrier materials. Therefore, polymers like PS[74], PEG[75] or

carbon nanotubes[76] as well as polymerized imidazolium salts[77] have been used. As

expected, supported hydroxy or carboxy functionalized imidazolium compounds gave

higher catalytic activity caused by their HB properties.[78] The immobilization of diol

functionalized ionic liquids (Figure 1.5, (a)) leads to further improvement of the reac-

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10

tivity, caused by the presence of two neighboring hydroxy groups as HB donors.[79]

Silica based materials represent another prominent class, regarding their use as car-

rier for imidazolium salt catalysts.[80] As mentioned previously, carboxy groups are

stronger HB donors than hydroxy groups, so that the epoxide is activated to a

stronger extent. This results in higher catalytic activity, which is also observed for

immobilized imidazolium salts on silica.[66] A recent approach from Zhang et al.

demonstrates the potential of silicon-based main-chain poly-imidazolium salts as cat-

alysts for cyclic carbonate synthesis.[81] In contrast to conventional heterogenized

imidazolium compounds, the Si-OH groups are located in the main-chain, leading to

higher catalytic activity at relatively mild conditions (Figure 1.5, (b)).[81] As environ-

mentally more benign alternatives, biopolymers like carboxymethylcellulose[82] or chi-

tosan (Figure 1.5, (c))[83] can be used as support materials. Due to the multiple HB

donor groups of the biopolymers, synergistic effects arise and high catalytic activities

are observed under relatively mild conditions.[82-83]

Figure 1.5: Supported imidazolium halide catalysts for the conversion of CO2 with epoxides to cyclic

carbonates.

Kleij et al. were able to reduce the required energy input by designing a heterogene-

ous catalyst based on a triazolium core immobilized on PS.[84] The attached pyrogal-

lol unit (Figure 1.6) efficiently activates the epoxide through HB, so that high catalytic

activities at mild reaction conditions are made possible (96 % PC, 45 °C, 10 bar CO2,

8 h). However, the catalyst has to be reactivated with methyl iodide after five recy-

cling runs, which is the major drawback of this system regarding the sustainability.[84]

Figure 1.6: Pyrogallol-functionalized triazolium iodide based catalyst for the cycloaddition of CO2 to

epoxides supported on a polystyrene resin.

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1. Introduction

11

1.1.3 Synergistic Binary Systems

In addition to tailor-made bifunctional catalysts, the combination of two suitable com-

pounds as mediators for the cycloaddition reaction represents an attractive alterna-

tive. Through proper choice of the respective single components, which are not or

only slightly catalytically active themselves, synergistic effects can be created, lead-

ing to highly reactive systems. In most of these cases one component activates the

epoxide through electrophilic interactions (mostly HB), while the second component

serves as nucleophile for the subsequent ring-opening. Because of this simple con-

cept and the easy accessibility of feasible single compounds, a myriad of combina-

tions is possible. Bioavailable amino acids,[85] as well as biopolymers like cellulose,[86]

lignin,[87] or cyclodextrin[88] bearing HB donor groups, are promising examples regard-

ing their sustainability. Combined with KI or superbases, e.g. DBU, non-toxic, com-

mercially available and relatively cost-efficient systems are obtained. However, de-

manding reaction conditions (> 100 °C, ≥ 10 bar CO2) have to be applied in order to

reach high cyclic carbonate yields in all cases. Regarding the reusability, L-

tryptophan (Figure 1.7, (a)) represents the only amino acid, which was proven to

show constant activity in five consecutive runs. But the related energy intensive vac-

uum distillation of the high boiling PC for isolating the KI/L-tryptophan system is its

major drawback.[85b] The recycling procedure is a great advantage of the biopolymer

based systems, as they are insoluble and can thus be recovered through simple fil-

tration. Consequently, e.g. the cyclodextrin system (Figure 1.7, (b)) can be recycled

with low energy input and thus minimized carbon footprint.[88] Initially, simple aliphatic

or aromatic hydroxy compounds were used for epoxide activation in binary catalyst

systems. It was found that phenol[89] and p-methoxy-phenol[90] can both act as suita-

ble catalysts. Nevertheless, later studies showed that multiple hydroxy HB donor

sites in spatial proximity have beneficial effects on the catalyst properties. Therefore,

catechol shows higher selectivity than phenol in combination with TBAB,[91] and eth-

ylene glycol gave superior catalytic activity compared to ethanol when used with KI

as nucleophile.[86b] By systematic screening of a variety of largely commercially avail-

able compounds together with TBAI, Kleij et al. revealed that three neighboring aro-

matic hydroxy groups enhance the catalytic activity significantly. Consequently, pyro-

gallol (Figure 1.7, (c)) was found as the most active epoxide activating agent, ena-

bling 96 % PC yield at room temperature (10 bar CO2, 18 h, 2.0 mol %). Further, DFT

studies have shown that multiple OH-groups have cooperative effects on the epoxide

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1. Introduction

12

activation and transition state or intermediate stabilization during the mechanism

(Scheme 1.4). Unfortunately, the catalyst system is not recyclable, which hinders it

from being sustainable.[73] A more promising example is the application of pentaeryth-

ritol (PETT, Figure 1.7, (d)) as multiple HB donor. In combination with TBAI, 96 % PC

yield at mild reaction conditions (70 °C, 4 bar CO2, 16 h) is enabled. Additionally, the

catalyst system is highly stable and can be easily recycled through precipitation with

diethyl ether, so that an energy demanding vacuum distillation is avoided. Moreover,

the individual components are non-toxic, cost-efficient and readily available, leading

to an overall highly sustainable system.[92]

Scheme 1.4: Mechanism of PO with CO2 catalyzed by pyrogallol as multiple HB donor in combination

with TBAI as nucleophile (cation removed for clarity).

As an innovative approach towards binary organocatalytic systems, Mattson et al.

used TBAI in combination with silanediols.[93] These are capable of recognizing the

epoxide, as well as the iodide through HB donor interaction. As a result, high catalytic

activities for various epoxides were observed with the optimized silanediol catalyst

(Figure 1.7, (e)) even under very mild reaction conditions (r.t.- 40 °C, 1 bar CO2,

18 h). In conclusion, this is a very promising approach regarding the carbon footprint

of the reaction, if the catalyst system is shown to be reusable in future works. If the

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1. Introduction

13

energetically disadvantageous vacuum distillation can be avoided during the recy-

cling procedure, an exceptional sustainable process is obtained.[93]

Figure 1.7: Selection of HB donor functionalized compounds used in combination with nucleophiles as

binary catalyst systems for the cycloaddition of epoxides with CO2.

1.2 Epoxidation of Olefins

1.2.1 Olefin Epoxidation in the Chemical Industry

The epoxidation of olefins is one of the most relevant transformations in the chemical

industry and in academia.[94] Epoxides are very important intermediates, mainly used

as monomers for the production of polyglycols, polyurethanes and polyamides.[95]

Also a multitude of fine chemicals, like pharmaceuticals[96] and surfactants[94c], are

synthesized using epoxides as feedstock. With an annual production capacity of

8 Mt/y in 2013 and an expected increase to approximately 9.6 Mt/y in 2018, PO rep-

resents one of the most important commodity chemicals.[97] The main challenge re-

garding industrial PO production poses the necessity of suitable mediators that allow

an economic process, as direct epoxidation in high yields is not yet possible with air

or oxygen.[98] Thus, a variety of reaction routes based on different mechanisms have

been developed (Scheme 1.5).[98] Through addition of hypochlorous acid to propene

and subsequent dehydrochlorination under basic conditions, propylene oxide (PO)

together with a great amount of harmful brine is obtained.[98-99] In the so-called

coproduct routes, hydroperoxides are generated in the first step through direct oxida-

tion of precursors (ethylbenzene, iso-butane, cumene) with oxygen. During the epox-

idation of propene, the corresponding alcohol is formed as coproduct, which can be

dehydrated to the related olefin.[100] To solve the problem of coproduct formation, the

cumene hydroperoxide process was developed, whereby the initial precursor is re-

covered through reduction of the coproduct.[101] Nevertheless, all of these approach-

es produce high amounts of by-products, thereby negatively affecting the environ-

mental benignity and economy of the process. After oxygen, aqueous H2O2 repre-

sents the oxidant with the second highest oxygen availability.[102] Moreover, in princi-

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1. Introduction

14

ple, water is generated as the only side product so that the amount of waste products

compared to produced PO can be decreased significantly. Thus, the HPPO (hydro-

gen peroxide propylene oxide) process was developed as state-of-the-art technolo-

gy.[98, 100] Using a titanium doped MFI type zeolite catalyst (TS-1) and MeOH as sol-

vent, 95 % PO selectivity under mild reaction conditions and > 99 % H2O2 conver-

sions are achievable.[103] With ≥ 0.3 t of H2O as the major byproduct, the energy in-

tensive purification of coproducts is redundant and the carbon footprint as well as the

economic efficiency are optimized. Additionally, the process runs continuously with

the heterogeneous catalyst packed in tubular reactors. The major drawbacks the

HPPO process suffers from are the high price of the titanium used for doping the zeo-

lite and the necessary regeneration of the TS-1 catalyst.[100]

Scheme 1.5: Reaction routes for the production of PO in the chemical industry.[98]

Besides the industrially used heterogeneous processes, vast numbers of homogene-

ous catalyst systems are described in literature.[95, 104] However, these are limited to

the synthesis of fine chemicals like enantiopure epoxides or other substrates requir-

ing highly selective approaches.[105] Nevertheless, molecular epoxidation catalysts

have a highly promising potential regarding their tunability and reactivity and are

hence extensively investigated especially in academia.[95]

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15

1.2.2 Multi-Phasic Olefin Epoxidation Using Ionic Compounds

Many high performance homogeneous catalysts have still not found their way to in-

dustrial applications because their separation from the products and reusability is

rather difficult and cost-intensive.[106] To solve this problem, the application of bipha-

sic catalysis is a promising route, enabling simple catalyst recycling for a plethora of

reactions.[107] The catalyst remains in one phase, while the products are located in

the other one, thus facilitating the separation procedure.[108] Due to their unique phys-

ical properties like low volatility, thermal stability and low flashing points, ionic liquids

(IL) possess some particular advantages over conventional organic solvents.[109] Ad-

ditionally, ILs often lead to enhanced reaction rates for several catalytic transfor-

mations.[110] As these features are also strongly influenced by the chemical structure

of the respective ions, they can be easily tuned towards the desired application, mak-

ing them extremely versatile.[111] Therefore, they are one of the most frequently used

solvent classes for liquid-liquid biphasic transformations, including the oxidation of

olefins.[112] The initial report dealing with olefin epoxidation in ILs was published by

Song and Roh.[113] By applying NaOCl as oxidant and a Mn(III)salen complex in a

mixture of DCM and an IL as solvent, a simple catalyst recycling procedure was

made possible.[113] Since then, numerous studies were presented dealing with transi-

tion metal epoxidation catalysts used in IL media. Most importantly, for Fe

porphyrin,[114] as well as for molybdenum complexes[115] and methyltrioxorhenium,[116]

the catalytic activity is enhanced by using ILs instead of conventional solvents. How-

ever, the water content in the ILs has to be considered when using sensitive transi-

tion metal complexes. Additionally, e g. [BF4]- or [PF6]

- containing ILs hydrolyze dur-

ing the reaction so that not all ILs can be used as suitable solvents when H2O2 is ap-

plied as oxidant.[117] HF is thus produced, leading to reduced selectivity through by-

product formation and decreased catalytic activity.[112]

Aqueous H2O2 as oxidant frequently results in biphasic reactions, as olefins are often

hydrophobic. Thus, the substrate is not located in the same phase as the oxidant and

catalyst, leading to a decrease of the reaction rate. Phase transfer catalysis (PTC) is

the most popular concept to ensure pronounced contact between the reaction part-

ners and thus enable high reaction rates in multi-phase systems.[118] Typically, ionic

compounds like quaternary ammonium salts are used as transfer reagent (TR), form-

ing an ion pair with an anionic reactant. An equilibrium between the organic and the

water phase is formed and the transferred anionic compound reacts in the organic

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1. Introduction

16

phase. In this process the reactant is activated by the lower degree of hydration.[119]

Nevertheless, this mechanism is not limited to ionic compounds as shown by Dehm-

low et al. for the extraction of H2O2 from aqueous solution in DCM or benzene

(Scheme 1.6, (a)). By applying TBAB or [N(n-hex)4]Br, a significant amount of H2O2

was transferred in the organic phase through HB interactions of the halide to the oxi-

dant. The amount extracted to the organic phase strongly depends on the cation, as

longer alkyl chains and thus more lipophilic ammonium salts resulted in higher H2O2

content.[120] Immense efforts concerning biphasic olefin epoxidation with aqueous

H2O2 combined with PTC were undertaken by the groups of Venturello and Ishii

through polyoxometalate (POM) catalysts.[121] The combination of phosphate and

tungstate or molybdate ions, respectively H3PW12 or H3PMo12 as catalyst precursors,

leads to water soluble peroxo intermediates upon treatment with aqueous H2O2.[122]

By addition of a long alkyl chain ammonium TR, this precursor is transferred to the

organic phase where it reacts with the lipophilic olefins (Scheme 1.6, (b)). The pre-

cursor is subsequently redissolved in the aqueous phase, closing the catalytic

cycle.[123]

Scheme 1.6: (a) Phase transfer of H2O2 by HB to quaternary ammonium salts[120]

and (b) biphasic

catalyst system using a transfer reagent (TR) as counter cation additive.[123]

Great research efforts were carried out to further improve this system in terms of

higher catalytic activity and reusability. For instance, by application of task-specific

ammonium salts, Zuwei et al. were able to prepare a reaction controlled self-

separating catalyst for propene epoxidation.[124] The salt precursor is insoluble in

aqueous phase or organic solvents but reacts with H2O2, forming a catalytic active

and organic soluble species. After consumption of H2O2, the insoluble catalyst pre-

cursor forms again, precipitates out of the reaction mixture and can thus be easily

recycled through filtration.[124] Therefore, propene, 1-hexene and cyclohexene can be

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17

converted under mild reaction conditions (35 °C – 65 °C ) with selectivites > 85 %

towards the epoxide and > 95 % H2O2 conversion.[124] The preparation of tetraalkyl-

ammonium salts of the divacant lacunary Keggin-type silica dodecatungstate

[γ-SiW10O36]8- under acidic conditions leads to alternative highly active catalysts. The

POM synthesized at pH 2 with TBAB was able to epoxidize a variety of olefins with

≥ 99% selectivity and H2O2 utilization efficiency and was recycled with constant ac-

tivity.[125] It is important to note that the catalytic activity of this type of compounds

strongly depends on the acidity of the reaction mixture used for the synthesis.[125]

Furthermore, acids are frequently used as an accelerator during catalysis.[123]

Besides the possibility to introduce transition metals to tune the catalytic properties of

POMs[94b], the substitution of ammonium salts with imidazolium moieties is a promi-

nent approach. By using [BMim] as countercation for [W10O23]4- or [PW12O40]

3- and

simultaneous application of the respective [BF4]- and [PF6]

- IL as solvent, easily reus-

able and highly active systems could be generated.[126] Utilization of an IL did not only

facilitate the recycling procedure, but also created a beneficial chemical environment

regarding the formation of the active species.[126] Hou et al. could further show that a

long chain imidazolium salt of a Ti substituted POM as heterogeneous epoxidation

catalyst clearly outperformed the TBA analog. This was ascribed to the higher flexibil-

ity and accessibility of the imidazolium catalyst.[127] The same group further accom-

plished a room temperature IL catalyst based on a dodecylimidazolium cation and a

tungstate POM, showing a reaction-induced phase separation behavior. Thereby, the

recycling procedure is significantly facilitated, as the catalyst separation can be con-

ducted through simple decantation.[128] A comparable effect can also be achieved by

using bisimidazolium salts bridged with a PEG unit as a countercation for the system

originally presented by Venturello et al.[129] More recently, Hou and coworkers used

the same imidazolium compounds for the synthesis of [W2O11]2- salts, thereby yield-

ing thermoregulated catalysts for olefin epoxidation with aqueous H2O2. Upon heating

the reaction mixture to the desired temperature, the catalyst dissolves in ethyl ace-

tate. After the epoxidation is completed, cooling to 0 °C leads to the precipitation of

the IL catalyst, whereby a separation by simple decantation is enabled. As a result,

the catalyst can be recycled efficiently and remains its activity for 17 consecutive

runs.[130] As aforementioned, a multitude of functional groups can be easily intro-

duced to the imidazolium moiety to design the properties towards the desired applica-

tion. This also applies for POM catalysts, where amino functionalized imidazolium

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18

cations can be used to synthesize heterogeneous Keggin-type catalyst analogs by

combination with H3PW12O40. The structure of this insoluble POM ionic hybrid con-

sists of nanospheres with partly protonated ammonium imidazolium cations and non-

protonated amino units. The authors assume that the amino-functionalized cations

interact with the POM anion through HB, which leads to superior catalytic activity

compared to imidazolium compounds without functional groups. Additionally, the HB

properties stabilize the nanosphere structure, leading to an easily recyclable insolu-

ble solid catalyst system.[131] Triethoxysilylpropyl wingtip modified imidazolium salts

can also be used to immobilize peroxotungstate as counter anion on silica supports.

Therefore, Mizuno et al. first prepared the respective [PF6]- salt, covalently anchored

the resulting IL on the carrier material and finally exchanged the anion with the POM.

The prepared heterogeneous catalyst was able to epoxidize a broad scope of sub-

strates and was recyclable through simple filtration with constant activity over four

runs.[132] Alternatively, vinyl substituted imidazolium salts can be used to synthesize

POM containing organic inorganic hybrid materials. In the first step mono- and divinyl

modified imidazolium bromide salts are radically copolymerized, while the POM unit

is subsequently introduced through anion exchange.[133] These heterogeneous cata-

lysts can be separated by filtration and are reusable without losing catalytic activity

for at least three runs.[133b] Apart from tungstate compounds, POM based on octamo-

lybdates are prepared in an easy and cost-efficient manner under acidic conditions

with defined pH values. Recently, it was found that POM bearing 1-hexyl-3-

methylimidazolium or 1-hexyl-2,3-dimethylimidazolium cations are applicable as self-

separating catalysts for the epoxidation of olefins using aqueous H2O2 as oxidant.[134]

The catalyst directly precipitates out of the reaction mixture upon completion of the

respective run, so that no addition of organic solvent is required. Followed by wash-

ing with water, the recovered catalyst is reused for the next catalytic cycle, thereby

showing nearly quantitative epoxide yield for at least ten consecutive runs (60 °C,

1 h, 1.5 mol %).[134] In order to facilitate the reaction procedure, carboxy functional-

ized imidazolium salts can be used to synthesize catalytic active molybdate based

POMs in situ.[135] Hence, the system is simplified considerably as the utilization of

additional acids becomes redundant. The catalytic activity depends on the pH value,

which is controlled by varying the carboxy-imidazolium/Na2WO4 ratio used for gener-

ating the catalyst. At tenfold excess of imidazolium salt, the optimum catalytic per-

formance was obtained and 68 % cyclooctene oxide yield could be achieved (60 °C,

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1. Introduction

19

24 h, 0.1 mol %). Moreover, the catalyst system could be reused for five runs with a

negligible loss of activity.[135]

1.2.3 Activation of H2O2 by Hydrogen Bonding

Conventionally, metal catalysts form peroxo species as active sites through reaction

with the oxidant. As an alternative, H2O2 in aqueous solution can be activated by

compounds forming HB. The initial studies dealing with alkene epoxidation solely

catalyzed by this mode of action were conducted by Neumann et al. using fluorinated

alcohol solvents as HB donors.[136] The strong electron withdrawing effect of the fluo-

rine substituents in combination with the HB donor ability of the hydroxy group leads

to the electrophilic activation of H2O2. The reactivity also depends on the degree of

fluorination, as 2,2,2-trifluoroethanol shows inferior catalytic activity compared to

1,1,1,3,3,-hexafluoroisopropyl alcohol (HFIP). Thus, the cyclooctene oxide yield could

be increased from 66 % to 99 % under the applied reaction conditions with HFIP as

solvent and epoxidation mediator (60 °C, 20 h).[136] Shortly afterwards, R. A. Sheldon

et al. confirmed the catalytic activity of these solvents and proved their inert nature

during the course of the reaction. Therefore, oxidation products are not involved in

the formation of the catalytic active species, meaning that only HB interactions are

responsible for H2O2 activation.[137] DFT calculations shed some light onto the mech-

anism and particularly on the role of HFIP, which was found to provide a complimen-

tary charge template for the transition state. Thus, the bond deformations are re-

duced and the electronic interactions between the fluorine residues and the hydrogen

atoms of the alkene and H2O2 stabilize the transition state (Figure 1.8, (a)).[138] The

influence of solvent clusters was revealed through kinetic investigations of the cata-

lytic performance, depending on the concentration of HFIP in the epoxidation of cis-

cyclooctene.[139] Significantly enhanced catalytic activity was only observed for high

HFIP concentrations, where coordination spheres of multiple HFIP molecules are

assumed to cause the rate acceleration.[139] Moreover, aggregates of HFIP and es-

pecially its di- and trimers show an elevated positive partial charge at the free hy-

droxy group and thus stronger HB donor properties.[140] On the basis of these results,

the mechanism of the HFIP catalyzed olefin epoxidation was reinvestigated by

Berkessel et al. with DFT methods.[141] It was shown that the energy activation barrier

decreased by approx. 15 kcal/mol, when two or three HFIP molecules are involved in

the reaction (Figure 1.8, (b,c)). This strongly suggests the participation of coordinated

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1. Introduction

20

HB networks during the catalytic cycle.[141] The major drawback regarding fluorinated

alcohols as catalytic active solvents is the large amount used for the reaction com-

bined with their extensive costs. To overcome this challenge, dendritic catalysts were

developed, which possess a high local concentration of fluororoalcohols on the poly-

mer surface. Hence, a comparable interaction to the multiple HB network of conven-

tional HFIP as solvent and high catalytic activity is enabled for olefin epoxidation with

aqueous H2O2. Consequently, 20 mol % HFIP analogs can be applied as substoichi-

ometric catalyst for quantitative cyclooctene oxide yield instead of using an excess of

HFIP as solvent.[142]

Figure 1.8: Possible transition states during the epoxidation of olefins with HB activated H2O2 involv-ing (a) one, (b) two or (c) three molecules of HFIP according to DFT calculations.

In addition to HB donors, it was shown that HB acceptors are capable of activating

H2O2 for the oxidation of sulfides to the respective sulfoxides.[143] Vibrational and

NMR spectroscopic studies have depicted that the [BF4]- anion of imidazolium salts

as solvent interacts with the hydrogen atoms of H2O2 through HB. Hence, the IL

serves as an activator, leading to a higher electrophilicity of the H2O2 oxygen atom

and participating in the cleavage of water as leaving group from the intermediate.[143]

More recently, it was firstly reported that HB acceptors are also able to mediate the

epoxidation of olefins with H2O2. Therefore, imidazolium perrhenates were synthe-

sized in high purities by a simple procedure using an anion exchange resin (AER).

The obtained ILs were used in equimolar amounts for the epoxidation of cis-

cyclooctene, whereby nearly quantitative conversion to the epoxide was observed

(70 °C, 4 h, 2.5 eq. aq. H2O2).[144] This is a counterintuitive result, as perrhenates

show no activity towards olefin epoxidation under common reaction conditions be-

cause of the interaction with the solvation shell.[145] To investigate the role of the

chemical environment on the catalytic performance in detail, NH4+, K+ and imidazoli-

um perrhenates were used as H2O2 activators for the epoxidation of cis-cyclooctene.

It was found that the imidazolium cation has a strong beneficial effect on the reaction

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1. Introduction

21

outcome, as the perrhenate anion is dissolved without the formation of a solvent

shell. Consequently, the HB acceptor ability of the perrhenate anion is not passivated

and a peroxide complex can be formed. The reaction mechanism was analyzed by

extensive IR, Raman and NMR spectroscopic studies. As the symmetry of [ReO4]-

changes after the addition of H2O2 from Td to C2v, while the local symmetry of the Re

center is unaffected, the formation of Re peroxo species was excluded. This was cor-

roborated by 17O labeled NMR spectroscopy. Therefore, the metal center is not in-

volved in the reaction and an outer sphere mechanism can be stated. The energeti-

cally most feasible scenario for the reaction mechanism was determined through DFT

calculations with ethene as a model substrate (Scheme 1.7). The first step involves

the formation of an outer-sphere complex between [ReO4]- and H2O2 through HB in-

teractions, thereby activating the oxidant. The extent of this effect is strongly influ-

enced by the polarity of the cation and thus the ion pairing. Subsequently, the transi-

tion state results from the addition of the olefin. Finally, an oxygen atom of the pre-

coordinated H2O2 is transferred to the olefin and the epoxide is obtained with water

as the only by-product. The IL mediators are also easily recyclable through extraction

with n-hexane and can be reused for at least eight consecutive without loss of activi-

ty. This clearly demonstrates their inertness under oxidative reaction conditions.[144]

Scheme 1.7: Mechanism of olefin epoxidation with H2O2 activated through HB to perrhenate

anions.[144]

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1. Introduction

22

However, equimolar amounts of imidazolium perrhenates have to be used to reach

quantitative conversions.[144] This is highly undesirable because of the costs associ-

ated with the rhenium containing counter anion. In order to improve their activity, the

easily tunable imidazolium moiety enables the tailoring of the IL properties, e.g. ion

pairing and solubility. This opens the possibility to use these compounds in catalytic

amounts, thereby decreasing the amount of rhenium in the reaction mixture.

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2. Objective of the Thesis

23

2 Objective of the Thesis

The main focus of this work was the development of organocatalytic systems for the

sustainable chemical fixation of CO2 as cyclic carbonates, which represent highly

desirable products. In contrast to the majority of organocatalysts reported in litera-

ture, the aim of the newly designed systems is to provide high catalytic activity at mild

reaction conditions (< 100 C, < 10 bar CO2). Thus, the carbon footprint of the process

can be minimized, thereby improving the overall sustainability. Although imidazolium

halides are frequently used organocatalysts for cyclic carbonate synthesis, the role of

the cation during the catalytic cycle has not been examined in detail. Therefore,

mechanistic investigations were carried out to understand the influence of the cation,

in order to design task-specific catalysts through structural optimization. Additionally,

binary synergistic catalyst systems were designed through combination of commer-

cially available compounds as epoxide activators with suitable nucleophiles. In this

process, simple, cost-efficient and sustainable systems for cyclic carbonate synthesis

should be enabled.

Scheme 2.1: Catalytic systems investigated within this work for the conversion of olefins to epoxides

and subsequent cycloaddition reaction with CO2 to the respective carbonate.

In the second part of this work, imidazolium molybdates and perrhenates were syn-

thesized and examined as catalysts for olefin epoxidation with aqueous H2O2 as oxi-

dant. Carboxy functionalized imidazolium salts were applied for the in situ synthesis

of catalytically active polyoxomolybdates. Hence, the reaction procedure was ex-

pected to be facilitated, as the need of additional acids for the catalyst preparation

prior to olefin epoxidation is eliminated. The key objective of the studies regarding

imidazolium perrhenates was to evaluate their potential as epoxidation catalysts and

to analyze the influence of the cation structure on the catalytic performance. By tailor-

ing of the imidazolium residue, it was intended to optimize the properties of these

ionic compounds and thus the catalytic activity. The long-term goal of this thesis is to

combine all findings to develop catalysts for the one-pot synthesis of cyclic car-

bonates from olefins, an oxidant and CO2 in a sustainable manner.

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3. Results – Publication Summaries

24

3 Results and Discussion

3.1 Publication Summaries

This chapter shortly summarizes the crucial aspects of the publications prepared dur-

ing the course of this dissertation. The bibliographic data of the complete manuscripts

can be found in Chapter 5 of this thesis.

3.1.1 Cycloaddition of CO2 and Epoxides Catalyzed by Imidazolium Bromides

under Mild Conditions: Influence of the Cation on Catalyst Activity

To evaluate the influence of the cation on the catalytic cycloaddition of CO2 to epox-

ides, systemically varied imidazolium bromides with different alkyl chain lengths and

aromatic residues were initially synthesized and characterized (Figure 3.1). There-

fore, 1H and 13C-NMR spectroscopy as well as elemental analysis were used, while

the structure of 10 was also determined by single X-ray diffraction. Subsequently, the

catalytic activity of the obtained series was tested under mild reaction conditions

(70 °C, 4 bar CO2, 22 h, 10 mol %) for the cycloaddition of CO2 with PO to PC.

Figure 3.1: Synthesized imidazolium bromide catalysts for PC formation (BzF5: 1-(2,3,4,5,6-pentafluoro)benzyl).

All investigated catalysts are liquid at 70 °C and thus able to dissolve CO2 under re-

action conditions. However, the difference of CO2 solubility in 4, 5, 6, 8 and 10 was

found to be insignificant so that an influence on the activity can be neglected. Re-

garding the impact of R2 on the catalytic activity for 1-3 and 4-6, it was shown that an

acidic C2 proton has a beneficial effect compared to an alkyl substituent. As free car-

benes can be excluded, because 2-3 and 5-6 are active although their C2 position is

alkylated, the HB properties of the C2 proton cause the higher catalytic activity. This

is supported by the improved reactivity upon modification with the electron withdraw-

ing fluorinated aromatic wingtip. Thus, the acidity of the C2 proton increases, leading

to a stronger HB donor ability and interaction strength. Consequently, 10 showed the

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3. Results – Publication Summaries

25

highest catalytic activity under the applied conditions. To investigate the HB interac-

tion of 10 in more detail, FTIR studies were performed upon addition of PO to the

neat catalyst at room temperature. The frequency of the vibration band at 3064 cm-1,

which is assigned to the stretching mode of the catalyst C2 proton, shifts by 24 cm-1

and broadens by a factor of 3 (Figure 3.2). This can be ascribed to intermolecular HB

of 10 to PO. As other imidazolium-ring vibrations are also shifted, it is difficult to ex-

actly specify which structural elements interact with PO. Nevertheless, the most pro-

nounced contact is observed between the acidic C2 proton and the oxygen atom of

PO, deriving from HB. On the basis of these results, the mechanism for PC formation

catalyzed by imidazolium halides bearing an acidic C2 proton is proposed (Scheme

3.1). The HB interaction weakens the PO C-H bond, thereby facilitating the nucleo-

philic ring-opening through the halide. Additionally, transition states and intermedi-

ates are stabilized, so that higher catalytic activity is observed. After optimization of

the reaction parameters (T, t, cat. loading), catalyst 10 was able to mediate PC for-

mation in 91 % yield at mild conditions (70 °C, 4 bar CO2, 22 h, 10 mol %). Moreover,

the recycling can be conducted through simple precipitation with remaining activity for

ten consecutive cycles. Aside from PO, a broad scope of epoxides can further be

converted to the respective cyclic carbonates applying 10 as catalyst. Thus, 10 rep-

resents a versatile and sustainable organocatalyst for the cycloaddition of epoxides

with CO2.

Scheme 3.1: Mechanism for the cycloaddition reaction

of PO with CO2 catalyzed by imidazolium halides.

Figure 3.2: FTIR spectrum of a) neat

catalyst 10 and b) 10 with excess of PO.

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3. Results – Publication Summaries

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3.1.2 Hydroxy-Functionalized Imidazolium Bromides as Catalysts for the Cy-

cloaddition of CO2 and Epoxides to Cyclic Carbonates

As previously mentioned, the acidic C2 proton of the imidazolium moiety synergisti-

cally interacts through HB during the mechanism of cyclic carbonate formation. Fur-

ther, organocatalysts with three hydroxy groups in spatial proximity are more efficient

compared to single or double functionalized analogs.[73, 84] Therefore, imidazolium

bromides with three (11-13) or two (14-16) HB donor sites were synthesized (Fig-

ure 3.3) and characterized by 1H, 13C-NMR, IR and mass spectroscopy as well as by

elemental analysis. Subsequently, the impact of the multiple HB donor sites was

evaluated through comparison of the catalytic activities with 1-10 and 17 as bench-

mark single HB donor based systems. In order to ensure a proper comparison, the

aforementioned mild reaction conditions (70 °C, 4 bar CO2, 10 mol % halide) were

also applied for 11-17.

Figure 3.3: Investigated catalysts to determine the impact of multiple HB donor sites on the activity.

It was shown that the variation of the wingtip residue results in an increased catalytic

activity in the order of Me < Bz < n-Oc (11-13). This is caused by the significantly

higher solubility of 13 in the reaction mixture. Additionally, 13 is the most active or-

ganocatalyst among the investigated compounds, as 95 % PC yield were observed

after 16 h. Consequently, the reaction time was reduced by 6 h compared to catalyst

10. The high catalytic activity arises from the triple HB donor motif (two acidic C2 pro-

tons and one hydroxy group), leading to an efficient epoxide activation and stabiliza-

tion of intermediates and transition states. The PC yields for the double HB analogs

14 and 16 amount to only 58 % and respectively 79 %, thereby underlining the posi-

tive effect of three neighboring HB sites. Compared to 17 as an ammonium based

benchmark system (92 % PC), the application of 13 further gave a slightly higher

yield under the applied conditions. Moreover, the catalytic activity of 13 was com-

pared with [HDBU]Cl as a state-of-the-art organocatalysts. As described in

literature,[46] more demanding conditions but shorter reaction times are used (140 °C,

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3. Results – Publication Summaries

27

10 bar CO2, 2 h, 1 mol %). In consequence, identical catalytic activity of 13 and

[HDBU]Cl was observed. For the potential application in larger scale and concerning

the sustainability, the recycling procedure and catalyst reusability are crucial. By ad-

dition of diethyl ether, 13 is easily precipitated from the reaction mixture and can be

reused after filtration. Hence, energy-intensive distillation of PC is avoided. As no

leaching phenomena or decomposition processes occur, the catalyst is reusable for

at least ten times without loss of activity. The facile recyclability demonstrates the

main advantage of catalyst 13 over 17 or [HDBU]Cl. Catalyst 13 can also be used for

the efficient conversion of a wide range of epoxides to their corresponding cyclic car-

bonates, including functionalized substrates. To shine some light onto the mecha-

nism for catalyst 13, DFT calculations were carried out, leading to the proposed cycle

shown in Scheme 3.2. It was confirmed that all HB donor sites show an interaction

during the mechanism. This leads to more efficient epoxide activation, a stabilization

of intermediates and thus a high catalytic activity. In conclusion, 13 is a very promis-

ing organocatalyst for cyclic carbonate formation under mild reaction conditions be-

cause of its high activity, stability and easy reusability. Therefore, the gap between

bifunctional and binary organocatalyst systems is minimized.

Scheme 3.2: Proposed mechanism for the cycloaddition of CO2 with PO catalyzed by 13.

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3. Results – Publication Summaries

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3.1.3 Niobium(V)chloride and Imidazolium Bromides as Efficient Dual Catalyst

Systems for the Cycloaddition of Carbon Dioxide and Propylene Oxide

The combination of the transition metal salt niobium(V)chloride (NbCl5)2 as Lewis

acid with nucleophiles like TBAB results in highly reactive catalyst systems for cyclic

carbonate formation. The metal center activates the epoxide through coordination to

the oxygen atom, which results in a polarized C-O bond and enhanced ring-opening

by the halide anion. Thus, the system shows high catalytic activity, even when the

reaction is carried out under ambient conditions. Herein, imidazolium bromides were

investigated as nucleophiles instead of using TBAB, with particular focus on the im-

pact of the imidazolium substitution pattern on the catalytic activity. Therefore, a se-

ries of 31 imidazolium bromides with varying aliphatic and aromatic residues (Fig-

ure 3.4) was synthesized and applied as a catalyst systems for PC formation in com-

bination with (NbCl5)2 (r.t., 4 bar CO2, 2 h).

Figure 3.4: Imidazolium bromides used as nucleophiles in combination with (NbCl5)2.

It was shown that the investigated imidazolium bromides with aliphatic residues gave

very high yields, whereby the catalytic activity varies in dependency of the R2 substit-

uent. In contrary to imidazolium bromides as single catalysts without involving Lewis

acids, the presence of an acidic C2 proton results in lower activities. Due to the

strong interaction of the metal center and PO compared to the C2 proton HB, addi-

tional activation of PO by the imidazolium cation is negligible. However, the ion-

pairing of the imidazolium moiety to the anion decreases upon C2 alkyl substitution

as the strong HB interaction site is eliminated. This leads to a lower degree of elec-

trostatic interaction, thus higher anion nucleophilicity and catalytic activity. As a re-

sult, the PC yield increases in the order of R2: H < Me ≤ Et ~ i-Pr~ n-Bu according to

the steric demand of the residue. The most active imidazolium bromide (R1: Me,

R2: i-Pr, R3: n-Bu) was used for the determination of the optimal catalyst loading and

ratio of NbCl5/nucleophile, which was found to be 1.0/2.0 mol-%. In situ IR measure-

ments further revealed that the imidazolium bromide/NbCl5 system constitutes con-

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3. Results – Publication Summaries

29

siderably higher turnovers in the beginning of the reaction compared to TBAB. But

during the course of the reaction, the activity of the imidazolium system drops quickly,

while the loss of activity for TBAB is less pronounced. This is ascribed to the shift of

the chemical environment from slightly polar (PO) to polar (PC).

The use of imidazolium bromides bearing aliphatic and aromatic residues generally

resulted in lower PC yields compared to cations exclusively substituted with aliphatic

side-chains. This is caused by the rather poor solubility in the reaction mixture.

Through introduction of BzF5, the solubility and catalytic activity could be increased

compared to the corresponding non-fluorinated Bz compounds. As observed for ali-

phatic cations, the substitution in C2 position leads to a higher catalytic activity due to

a lower degree of ion pairing. As a result, the same order of reactivity was observed

for the respective R2 residues. Finally, combinations of (NbCl5)2 with imidazolium

bromides bearing two aromatic wingtips were used as catalyst systems for PC syn-

thesis, leading to poor conversions. Due to the formation of Coulomb networks, which

are comparatively stable because of the aryl substituents, these imidazolium bro-

mides are barely soluble in the reaction mixture. Nevertheless, it was confirmed that

alkyl substitution in C2 position leads to enhanced catalytic activity because of the

reduced electrostatic interaction between the ions. Additionally, fluorination of the

aromatic rings again leads to a higher solubility and activity. The

(NbCl5)2/imidazolium bromide catalyst system was also applied for the conversion of

a variety of epoxides to their cyclic carbonates. The reaction conditions were chosen

according to the previously studied (NbCl5)2/TBAB system (40 °C and 8 h).[25a] The

investigated aliphatic and aromatic epoxides were converted efficiently with the ex-

ception of epichlorohydrin. The chloro group presumably interacts with the metal cen-

ter and therefore competes with the oxygen atom of the epoxide.

In summary, combinations of imidazolium bromides with (NbCl5)2 enable high catalyt-

ic activities under very mild reaction conditions. The Lewis acidic metal center acti-

vates the epoxide and the imidazolium bromide provides the nucleophile for subse-

quent ring-opening. The ion pairing and the solubility are the main factors that affect

the catalytic activity regarding the imidazolium structure. Whereas C2 alkyl substitu-

tion results in decreased ion pairing and higher catalytic activity, alkyl wingtips lead to

better solubility and conversions in comparison to aryl residues.

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3.1.4 Cycloaddition of Carbon Dioxide and Epoxides Using Pentaerythritol and

Halides as Dual Catalyst System

Combinations of PETT and a variety of halide based nucleophiles, like TBAI, were

used as binary organocatalysts to synthesize cyclic carbonates (Scheme 3.3).

Scheme 3.3: Cyclic carbonate synthesis using PETT/Nu as binary organocatalytic system.

The cycloaddition of PO and CO2 was used to determine the influence of the pres-

ence of both compounds and the nature of the nucleophilic component on the reac-

tivity. It was clearly shown that synergistic effects are responsible for the activity as

no or very small conversions are observed when only PETT or TBAI are used as sin-

gle catalysts. This is ascribed to the HB abilities of PETT, leading to lower energy

barriers for epoxide ring-opening and the stabilization of intermediates and transitions

states. Thus, the reaction can be carried out with excellent conversions under mild

reaction conditions (70 °C, 4 bar CO2) with PETT/TBAI as a binary system. Further,

the catalytic activity strongly depends on the cation of the halide nucleophile. Using

KI instead of TBAI significantly reduces the PC yield from 96 to 6 % under the inves-

tigated conditions. This derives from the lower degree of ion pairing in TBAI, leading

to higher anion nucleophilicity and catalytic activity. Moreover, imidazolium bromides

were used as nucleophilic components to investigate the role of the cation in more

detail, whereby lower catalytic activities were observed. On the one hand, this arises

from the higher bulkiness of the tetrabutylammonium cation, resulting in higher nu-

cleophilicity. On the other hand, the imidazolium cation also bears HB sites, which

presumably stabilize the halide anion and compete with the hydroxy groups of PETT.

This is supported by the higher yields obtained when C2- or tetramethyl-substituted

imidazolium analogs with weaker HB donor abilities are used in this binary system.

Both TBAI and TBAB lead to nearly quantitative yields in combination with PETT after

22 h and thus, superior catalytic activity compared to the other cations investigated.

Therefore, time dependent analysis of the PC yield was carried out with TBAI and

TBAB in order to examine the influence of the anion on the reactivity. At any time of

the reaction, the yields of the TBAI system were higher compared to TBAB. As the

bromide anion possesses a stronger HB acceptor effect, the interaction strength to

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0

20

40

60

80

100

1 2 3 4 5 6 7 8

PC

yie

ld [

%]

No. of catalytic cycles

PETT is higher compared to iodide. As a result, it is stabilized to a greater extent and

is less nucleophilic and reactive. Additionally, the activation of the epoxide through

PETT is hindered because of the more pronounced competitive HB of bromide com-

pared to iodide. Consequently, the reaction time can be decreased from 22 h for

PETT/TBAB to 16 h for PETT/TBAI. By systematic variation of the temperature and

the catalyst loading, the reaction conditions were further optimized. Finally 96 % PC

yield could be achieved at 70 °C by using 5.0 mol-% of PETT and TBAI.

The reusability and the recycling procedure are crucial regarding the catalyst sus-

tainability. Especially binary organocatalysts like pyrrogallol/TBAI are consumed or

decompose during the reaction, so that the activity drops already in the second run.

However, this not observed for the PETT/TBAI catalyst system, which can be reused

for at least eight runs with remaining activity (Figure 3.5, (a)). In addition, the separa-

tion from the reaction mixture is conducted by simple precipitation with diethyl ether

and subsequent filtration, so that energy intensive distillation is avoided. Moreover,

PETT/TBAI converts a broad scope of substrates efficiently to their respective cyclic

carbonates. Besides aromatic and aliphatic epoxides, the system also tolerates func-

tional groups (Figure 3.5 (b), Entry 4 and 5) and thus covers a wide range.

Conclusively, the PETT/TBAI binary organocatalyst system efficiently mediates the

cycloaddition reaction of epoxides with CO2 under mild reaction conditions. It consists

of cost-efficient, commercially available and non-toxic components and is easily re-

usable for eight consecutive runs without loss of activity. Therefore, it represents an

exceptional sustainable approach towards cyclic carbonate synthesis using CO2.

Figure 3.5: (a) Influence of the PETT/TBAI catalyst recycling on the PC yield and (b) conversions of different substrates, selectivities ≥ 99 % for all investigated epoxides (reaction conditions in both cas-es: 70 °C, 4 bar CO2, 16 h, 10 mmol epoxides and 0.5 mmol catalysts).

(a) (b)

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3.1.5 Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in situ

in Ionic Liquids

Carboxy-functionalized ILs were used for the in situ formation of a catalyst system

based on polyoxomolybdates. The resulting system was tested for the epoxidation of

cis-cyclooctene using aqueous H2O2 (Scheme 3.4). Consequently, organic acids,

usually used for adjusting the pH value, can be avoided, leading to facilitated catalyst

preparation.

Scheme 3.4: Catalytic epoxidation of cis-cyclooctene with polyoxomolybdates prepared in situ.

In order to find the optimum reaction conditions, the ratio IL to molybdate, the molyb-

date concentration itself and the reaction temperature were systematically varied. As

expected, the catalytic activity is strongly influenced by the amount of acid-

functionalized IL because the pH value controls the structure of the formed polyoxo-

molybdates. By adjusting the pH value to 3.5, corresponding to an IL/molybdate ratio

of 10/1, the highest catalytic activity was observed. It is supposed that these condi-

tions result in the formation of [MoxOy]2- clusters, which are responsible for the cata-

lytic activity. Moreover, no cyclooctene-1,2-diol is formed so that the selectivity for all

reactions amounts to > 99%. The molybdate concentration in the reaction mixture

also heavily impacts the catalytic activity. In absence of a molybdate precursor, the

olefin conversion drops rapidly, so that peracids as potential alternative catalytic ac-

tive species can be excluded. Besides, using an excess of molybdate also gave a

decreased cyclooctene oxide yield because of the solubility behavior. The resulting

slurry of undissolved sodium molybdate rapidly decomposes H2O2 and thus, low

yields are observed. Finally, a catalyst loading of 5.0 mol % was found as the opti-

mum value regarding the catalytic activity of the system. Furthermore, variations of

the reaction temperature were found to substantially affect the outcome of the reac-

tion (Figure 3.6, (a)). This can be attributed to changes in the solubility behavior of

the polyoxometalate in the water/IL phase and the olefin in the reaction mixture. At

T < 50 °C a slurry was formed because of the solubility of the IL in the aqueous

phase. When the temperature was increased to 70 °C, the H2O2 decomposition is

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0

20

40

60

80

100

1 2 3 4 5 6

yie

ld [

%]

no. of catalytic cycles

0

20

40

60

80

100

20 30 40 50 60 70

yie

ld (

%)

temperature (°C)

15 min 1 h 4 h 24 h

presumably the favored reaction route, as strong gas evolution was observed. Final-

ly, a reaction temperature of 60 °C gave the highest cyclooctene oxide yield among

the investigated reaction conditions. With the optimum reaction conditions in hand

(60 °C, 24 h, 1.5 eq. H2O2, IL/Na2MoO4: 10.0/1.0 mol %), the recycling procedure and

reusability of the catalyst system were investigated. Therefore, the organic phase

containing the product was extracted with n-hexane and separated from the aqueous

phase, which was simply dried in high vacuum at 80 °C. Consequently, the catalyst

system could be reused for six reaction runs with negligible loss of activity (Figure

3.6, (b)).

The epoxidation of cis-cyclooctene can be conducted under relatively mild reaction

conditions, using the in situ prepared catalyst system. Although the system is not as

active as molecular systems, the use of readily available and cost-efficient precursors

and the reusability without considerable loss of activity are attractive aspects.

Figure 3.6: (a) Effect of the reaction temperature and reaction time on the cyclooctene oxide yield (2.00 mmol cis-cyclooctene, 0.1 mmol Na2MoO4, 1.0 mmol IL, 3 mL deionized water); (b) reusabil-ity of the catalyst system for cis-cyclooctene epoxidation (60 °C, 24 h).

(a) (b)

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3.2 Epoxidation of Olefins Using Ionic Liquids as Phase Transfer Cata-

lysts

3.2.1 Results and Discussion

As mentioned in Chapter 1.2.3, equimolar amounts of imidazolium perrhenates are

able to mediate the epoxidation of cis-cyclooctene using aqueous H2O2 as oxidant.

Due to the chemical environment created by the IL, the [ReO4]- anion is capable of

activating H2O2 by HB, leading to a facilitated oxygen atom transfer to the olefin.

Herein, imidazolium perrhenates as olefin epoxidation catalysts were investigated for

the first time. In particular, the influences of the imidazolium cation on the environ-

ment, e.g. solubility, ion pairing and thus, on the catalytic activity, were investigated.

Therefore, various alkyl substituted imidazolium perrhenates were synthesized

(Scheme 3.5) using a literature known procedure based on halide anion exchange to

the corresponding hydroxide.[144] By conversion with ammonium perrhenate, the tar-

get compounds are finally obtained together with water and ammonia as the only by-

products.

Scheme 3.5: Synthesis procedure and overview of all synthesized imidazolium perrhenate catalysts

within this work (AER: anion exchange resin).

The catalytic activity was investigated with cis-cyclooctene as a model substrate and

50 wt. % aq. H2O2 (Table 3.1) as the oxidant. It is noteworthy that the selectivity for

cyclooctene oxide was ≥ 99 % for all investigated catalysts as no epoxide ring-

opening was detected.

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Table 3.1: Epoxidation of cis-cyclooctene catalyzed by imidazolium perrhenates.

Catalyst R3 R2 Yield [%] after 4 h[a] Yield [%] after 24 h[a]

18 Me H 3 22

19 Me Me 4 60

20 Me n-Bu 5 60

21 n-Bu H 7 55

22 n-Bu Me 8 70

23 n-Bu n-Bu 24 100

24 n-Oc H 44 98

25 n-Oc Me 88 100

26 n-Oc n-Bu 21 34

27 n-Do H 64 96

28 n-Do Me 85 100

29 n-Do n-Bu 2 8

Reaction conditions: 10 mmol cis-cyclooctene, 0.5 mmol catalyst (5.0 mol %),

25 mmol aq. H2O2 (50 wt. %), T = 70 °C; [a] yields based on GC analysis.

Regarding the influence of the substitution pattern on the reaction outcome, it was

found that imidazolium cations with short alkyl wingtips and a C2 proton result in low

activities (Table 3.1, catalysts 18, 21). The strong HB donor ability of the acidic C2-H

presumably causes a high degree of ion pairing to [ReO4]-. Thus, the activation of

H2O2 by the anion as HB acceptor is hindered, leading to low conversions. However,

alkyl chains in R2 position do not enhance the catalytic activity significantly (Ta-

ble 3.1, catalysts 19, 20, 22, 23). Consequently, the electrostatic interaction between

the ions is not the only factor affecting the activity of the catalyst. As wingtip substitu-

tion with elongated alkyl chains leads to substantially improved activity (Table 3.1,

catalysts 24, 25, 27, 28), the hydrophobicity of the IL catalysts is another key factor.

Nevertheless, a n-Bu residue in C2 position results in a strongly decreased catalytic

activity in these cases (Table 3.1, catalysts 26, 29), presumably because of the too

high hydrophobicity. However, the corresponding C2 methylated analogs represent

the most active epoxidation catalysts among the investigated compounds (Table 3.1,

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Figure 3.7: (a) cis-cyclooctene solubility in a mixture of 0.5 mmol catalysts and 25 mmol 50 wt. % aqueous H2O2; (b) time-dependent conversion of cis-cyclooctene with IL catalysts 24, 25 and 26 (10 mmol cis-cyclooctene, 0.5 mmol ILs, 70 °C, 2.5 eq. H2O2).

catalysts 25, 28). They exhibit the proper solubility behavior and the degree of ion

pairing is low, thereby enabling efficient activation of H2O2 by [ReO4]- as HB acceptor.

To understand the impact of the hydrophobicity on the activity in detail, the quantita-

tive solubility of the R3: n-Oc series was determined in cis-cyclooctene, water and

aqueous H2O2. The investigated ILs are almost insoluble in cis-cyclooctene

(< 50 ppm) and only barely soluble (24, 2 wt. %, 25, 1 wt. %) or even insoluble (26) in

water. These solubilities change drastically in presence of the oxidant in the aqueous

phase. Whereas the behavior of 26 remains unchanged, 24 is entirely soluble and

25 wt. % of 25 are dissolved in 50 wt. % aq. H2O2. Consequently, 24 and 25 are en-

tirely dissolved in the aq. H2O2 phase under catalytic conditions, which is caused by

the strong HB interactions of [ReO4]- to H2O2. Moreover, the solubility of cis-

cyclooctene in the biphasic system is affected by the ILs (Figure 3.7, (a)). Compared

to the absence of IL, the substrate solubility in aq. H2O2 under reaction conditions is

enhanced by the factor of 50 using 24, and 20 for 25. In contrast, addition of 26 even

lowers the olefin solubility in aq. H2O2 because of the three-phasic reaction mixture.

Thus, the most active catalyst 25 (Figure 3.7, (b)) is entirely soluble in aq. H2O2 and

is able to transfer the substrate in the aqueous phase. Further, the alkyl substitution

in C2 position leads to low electrostatic interactions between the ions, which in turn

enables more pronounced HB to H2O2 and therefore a more efficient activation.

For the investigation of the stability and the reusability of the catalysts, 24 and 25

were used as test compounds. After the recycling by extraction and subsequent dry-

(b) (a)

0

0.05

0.1

0.15

0.2

0.25

24 25 26

[wt.

-%]

0

20

40

60

80

100

0 1 2 3 4

co

nve

rsio

n[%

]

time [h]

25

24

26

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ing in vacuum, the next catalytic run was started under standard conditions and 4 h

reaction time. No decomposition reactions or leaching was observed and at least ten

consecutive runs were possible without loss of activity (Figure 3.8).

Figure 3.8: Yields of cyclooctene oxide for ten consecutive reaction with catalyst 24 and 25, reaction conditions: 10 mmol cis-cyclooctene, 25 mmol aq. H2O2 (50 wt.%), 0.5 mmol catalysts, 4 h, 70 °C.

In addition, catalyst 25 was used for the oxidation of various olefins with aqueous

H2O2 as oxidant. Given the different reactivities and solubilities of substrates other

than cis-cyclooctene, more demanding reaction conditions were applied (70 °C, 24 h,

2.5 eq. H2O2, 20 mol % catalyst loading). All tested substrates could be efficiently

converted, albeit to the corresponding diol products (Table 3.2). This derives from the

higher sensitivity towards nucleophilic ring-opening of the respective epoxides com-

pared to cyclooctene oxide. To challenge this problem, the structure of the applied

imidazolium perrhenate catalysts can be individually tuned for each substrate, which

will be the subject of future investigations.

Table 3.2: Epoxidation of various olefins with catalyst 25.[a]

Substrate Conversion [%][b] Selectivity Diol [%][b]

1-Octene ≥ 99 % ≥ 99 %

Styrene ≥ 99 % ≥ 99 %

Allyl alcohol ≥ 99 % ≥ 99 %

Cyclohexene ≥ 99 % ≥ 99 %

[a] Reaction conditions: 10 mmol olefin, 2.0 mmol catalyst (20 mol %), 25 mmol aq.

H2O2 (50 wt. %), T = 70 °C; 24 h; [b] conversions and selectivities determined by

integration of the olefin, diol and epoxide peaks in the 1H NMR spectra.

0

25

50

75

100

1 2 3 4 5 6 7 8 9 10

yie

ld [

%]

no. of catalytic runs

■ 24

■ 25

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In summary, these studies have shown for the first time that imidazolium perrhenates

can be used as catalysts for the epoxidation of unfunctionalized olefins with aq. H2O2.

The catalytic activity is strongly influenced by the interactions between the ions and

the catalyst hydrophobicity, which can both be controlled by systematic variation of

the imidazolium pattern. Upon substitution of the C2 position with alkyl residues, the

degree of ion pairing decreases, while the HB acceptor interaction strength of [ReO4]-

to H2O2 is enhanced. In order to allow a pronounced contact, the catalyst has to be

soluble in the aqueous phase containing the oxidant. However, good activity is only

achieved when the catalyst transfers the olefinic substrate in the aqueous phase,

where the reaction takes place. Thus, the cation hydrophobicity has to be properly

tuned so that the imidazolium perrhenate is soluble in aqueous H2O2 and is simulta-

neously able to act as phase transfer catalyst.

3.2.2 Experimental Details

All syntheses and catalytic reactions were carried out under air, if not stated other-

wise. 1,2-Dimethylimidazole, hydrogen peroxide (50 % in water), n-hexane, acetoni-

trile, ethyl acetate were purchased from Acros Organics. NaOH pellets were pur-

chased from J. T. Baker. 1-Bromobutane, 1-bromooctane and 1-bromododecane

were received from Merck. Cis-cyclooctene (95 %), acetone and Amberlite IRA-400

(OH) were purchased from Sigma-Aldrich. All chemicals were used as received with-

out further purification.

Analytical Equipment

1H- and 13C-NMR spectra were recorded on a 400 MHz Bruker Advance DPX-400

spectrometer and calibrated to the corresponding solvent signals (CDCl3: 7.26 ppm

for 1H, 77.16 ppm for 13C; DMSO: 2.50 ppm for 1H, 39.52 ppm for 13C). Microanalysis

was performed at the Mikroanalytisches Labor of the Technische Universität Mün-

chen in Garching. The melting points were determined with a MPH-H2 melting point

meter from Schorpp Gerätetechnik. Catalytic runs were performed on a cycler “Car-

ousel 12 plus” from Radleys and monitored via GC methods on a Hewlett-Packard

HP 5890 Series II instrument equipped with a FID, Superlco column Alphadex 120

and a Hewlett-Packard integration unit HP 3396 Series II.

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Experimental Procedure for Catalytic Olefin Epoxidation

The corresponding catalyst (0.5 mmol or 2.0 mmol) was placed in a glass tube

equipped with a magnetic stirring bar. Subsequently, the substrate (10.0 mmol) was

added and the reaction mixture was heated to 70 °C. Finally, the oxidant (25.0 mmol)

was added and the reaction mixture was kept at 70 °C for 4 and 24 hours. Continu-

ous samples (0.1 mL) were taken from the top phase (substrate and product), mixed

with an internal standard (1.0 mL) and analyzed by GC for cis-cyclooctene. The reac-

tion outcome for all other substrates was determined by integration of the olefin, diol

and epoxide peaks in the 1H-NMR spectra.

Experimental Procedure for Catalyst Recycling

Recycling experiments were performed in a round-bottomed flask equipped with a

magnetic stirring bar under the same conditions as mentioned above. After each run,

cis-cyclooctene and cyclooctene oxide where extracted at 70 °C with n-hexane

(2 x 2.5 mL). The residual solvent, water and hydrogen peroxide were subsequently

removed under reduced pressure at 70 °C for of 4 h.

Solubility Measurements

The solubility measurements were performed by Dipl.-Chem. Johannes Schäffer at

the Chair of Chemical Engineering of Prof. Dr.-Ing. Andreas Jess at the Faculty of

Engineering Sciences from the University of Bayreuth.

3.2.3 Synthesis and Characterization of the Catalysts

Preparation of Imidazolium Bromides

The imidazolium bromides and iodides (for 18, 19 and 20) were synthesized accord-

ing to literature procedures.[25b, 146] The purity of the compounds was determined with

1H- and 13C-NMR spectroscopy as well as with elemental analysis.

Preparation of Imidazolium Perrhenate Catalysts

The imidazolium perrhenates were prepared according to a literature known proce-

dure.[144] The previously synthesized imidazolium bromides were first transformed to

the corresponding hydroxide analogs through an anion exchange resin. Subsequent-

ly, an excess of NH4ReO4 (1.10 eq.) was added and the resulting reaction mixture

was stirred at 70 °C for 24 h leading to water and ammonia as only by-products. Af-

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terwards, all volatiles were removed in high vacuum at elevated temperatures and

dichloromethane was added to the resulting mixture of imidazolium perrhenate and

excess of NH4ReO4. Finally, the insoluble NH4ReO4 was filtered off and the target

catalyst was received after removing the volatiles in vacuo. The purity of the synthe-

sized compounds was analyzed by means of 1H-, 13C-NMR and IR spectroscopy, as

well as with elemental analysis and melting point determination.

Characterization Data

1,3-Dimethylimidazolium perrhenate (18):

C5H9N2O4Re (347.34 g/mol); colorless powder; 89 % yield; m.p.: 90 °C;

1H NMR ([d6]DMSO, 400 MHz, RT, ppm): δ = 9.02 (s, 1H, CH), 7.67 (d,

3J(H,H) = 2 Hz, 2 H, CH), 3.84 (s, 6H, CH3);

13C-NMR (100.28 MHz, CDCl3, RT, ppm) δ = 137.0, 123.5, 35.7;

IR (ATR, diamond crystal, neat): v = 905 (Re=O asymmetric);

Elemental analysis calcd. (%) for C5H9N2O4Re: C 17.29, H 2.61, N 8.07, O 18.42,

Re 53.61; found: C 17.77, H 2.70, N 8.15, Re 52.75.

1,2,3-Trimethylimidazolium perrhenate (19):

C6H11N2O4Re (361.37 g/mol); colorless powder; 33 % yield; m.p.: 191 °C;

1H NMR ([d6]DMSO, 400 MHz, RT, ppm): δ = 7.24 (s, 2H, CH), 3.92 (s, 6H, CH3),

2.76 (s, 3H, CH3);

13C-NMR ([d6]DMSO, 100 MHz, RT, ppm) δ = 144.8, 122.0, 34.8, 9.2;

IR (ATR, diamond crystal, neat): v = 900 (Re=O asymmetric);

Elemental analysis calcd. (%) for C6H11N2O4Re: C 19.94, H 3.07, N 7.75, O 17.71,

Re 51.53; found: C 20.10, H 2.98, N 7.72, Re 51.63.

2-Butyl-1,3-dimethylimidazolium perrhenate (20):

C9H17N2O4Re (403.45 g/mol); colorless powder; 86 % yield; m.p.: 93 °C;

1H NMR ([d6]DMSO, 400 MHz, RT, ppm): δ = 7.60 (s, 2H, CH), 3.79 (s, 6H, CH3),

2.99 (t, 3J(H,H) = 8 Hz, 2H, CH2), 1.60-1.50 (m, 2H, CH2), 1.42-1.30 (m, 2H, CH2),

0.91 (t, 3J(H,H) = 7 Hz, 3H, CH3);

13C-NMR ([d6]DMSO, 100 MHz, RT, ppm) δ = 144.8, 122.0, 34.8, 9.2;

IR (ATR, diamond crystal, neat): v = 897 (Re=O asymmetric);

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Elemental analysis calcd. (%) for C9H17N2O4Re: C 26.79, H 4.25, N 6.94, O 15.86,

Re 46.15; found: C 26.99, H 4.25, N 6.95, Re 45.92.

1-Butyl-3-methylimidazolium perrhenate (21):

C8H15N2O4Re (389.42 g/mol); yellow liquid; 86 % yield;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ= 8.92 (s, 1 H, CH), 7.39 (s, 1 H, CH), 7.36 (s,

1 H, CH), 4.24 (t, 3J(H,H) = 8 Hz, 2 H, CH2), 4.02 (s, 3 H, CH3), 1.89-1.81 (m, 2 H,

CH2), 1.39-1.30 (m, 2 H, CH2), 0.97 (t, 3J(H,H) = 7 Hz, 3 H, CH3);

13C NMR (CDCl3, 100 MHz, RT, ppm) δ = 136.5, 123.9, 122.5, 50.3, 36.7, 32.1, 19.6,

13.5;

IR (ATR, diamond crystal, neat): v = 892 (Re=O asymmetric);

Elemental analysis calcd. (%) for C8H15N2O4Re: C 24.67, H 3.88, N 7.19, O 16.43,

Re 47.82; found: C 24.98, H 3.81, N 7.06, Re 43.38.

3-Butyl-1,2-dimethylimidazolium perrhenate (22):

C9H17N2O4Re (403.45 g/mol); colorless powder; 90 % yield; m.p.: 68 °C

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 7.28 (d, 3J(H,H) = 2 Hz, 1H, CH), 7.22 (d,

3J(H,H) = 2 Hz, 1H, CH)), 4.12 (t, 3J(H,H) = 8 Hz, 2H, CH2), 3.89 (s, 3H, CH3), 2.70

(s, 3H, CH3), 1.84-1.76 (m, 2H, CH2), 1.42-1.35 (m, 2H, CH2), 1.00 (t, 3J(H,H) = 7 Hz,

3H, CH3);

13C-NMR (CDCl3, 100 MHz, RT, ppm) δ = 149.6, 122.8, 121.1, 48.9, 35.5, 31.7, 19.8,

13.7, 9.7;

IR (ATR, diamond crystal, neat): v = 898 (Re=O asymmetric);

Elemental analysis calcd. (%) for C9H17N2O4Re: C 26.79, H 4.25, N 6.94, O 15.86,

Re 46.15; found: C 26.73, H 4.19, N 6.84, Re 46.90.

1,2-Dibutyl-3-methylimidazolium perrhenate (23):

C12H23N2O4Re (445.53 g/mol); red oil; 80 % yield;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 7.36 (s, 1H, CH), 7.31 (s, 1H, CH), 4.09 (t,

3J(H,H) = 8 Hz, 2H, CH2), 3.88 (s, 3H, CH3), 3.00 (t, 3J(H,H) = 8 Hz, 2H, CH2), 1.83-

1.75 (m, 2H, CH2), 1.63-1.55 (m, 2H, CH2), 1.50-1.35 (m, 4H, CH2), 0.98 (t, 3J(H,H) =

8 Hz, 6H, CH3);

13C-NMR(CDCl3, 100 MHz, RT, ppm) δ = 146.9, 123.2, 121.1, 48.5, 35.3, 32.1, 29.2,

23.1, 22.6, 19.8, 13.7, 13.6;

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IR (ATR, diamond crystal, neat): v = 894 (Re=O asymmetric);

Elemental analysis calcd. (%) forC12H23N2O4Re: C 32.50, H 4.77, N 6.32, O 14.43,

Re 41.98; found: C 32.47, H 5.07, N 6.21, Re 41.89.

1-Methyl-3-octylimidazolium perrhenate (24):

C12H23N2O4Re (445.53 g/mol); pale yellow liquid; 90 % yield;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 8.85 (s, 1 H, CH), 7.41 (s, 1 H, CH), 7.36

(s, 1 H, CH), 4.20 (t, 3J(H,H) = 8 Hz, 2 H, CH2), 4.00 (s, 3 H, CH3), 1.89-1.79 (m, 2 H,

CH2), 1.35-1.20 (m, 10 H, CH2), 0.84 (t,3J(H,H) = 8 Hz, 3 H, CH3);

13C NMR (CDCl3, 100 MHz, RT, ppm) δ = 136.2, 124.0, 122.5, 50.5, 36.6, 31.7, 30.2,

29.0, 28.9, 26.3, 22.6, 14.1;

IR (ATR, diamond crystal, neat): v = 895 (Re=O asymmetric);

Elemental analysis calcd. (%) for C12H23N2O4Re: C 32.35, H 5.20, N 6.29, O 14.36,

Re 41.79; found: C 32.60, H 5.30, N 6.31, Re 42.53.

1,2-Dimethyl-3-octylimidazolium perrhenate (25):

C12H25N2O4Re (459.56 g/mol); pale yellow oil; 87 % yield;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 7.33 (d, 3J(H,H) = 2 Hz, 1H, CH), 7.25 (d,

3J(H,H) = 2 Hz, 1H, CH), 4.09 (t, 3J(H,H) = 8 Hz, 2H, CH2), 3.87 (s, 3H, CH3), 2.67 (s,

3H, CH3), 1.81-1.71 (m, 2H, CH2), 1.40-1.20 (m, 10H, CH2), 0.86 (t, 3J(H,H) = 7 Hz,

3H, CH3);

13C-NMR (CDCl3, 100 MHz, RT, ppm) δ = 143.7, 122.7, 120.9, 48.8, 35.3, 31.6, 29.6,

28.9, 26.3, 22.5, 14.0, 9.5;

IR (ATR, diamond crystal, neat): v = 895 (Re=O asymmetric);

Elemental analysis calcd. (%) for C12H25N2O4Re: C 33.98, H 5.48, N 6.10, O 13.93,

Re 40.52; found: C 34.00, H 5.42, N 6.05, Re 40.50.

2-Butyl-1-methyl-3-octylimidazolium perrhenate (26):

C16H31N2O4Re (501.64 g/mol); colorless powder; 85 % yield; m.p.: 53 °C;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 7.33 (d, 3J(H,H) = 2 Hz, 1H, CH), 7.28 (d,

3J(H,H) = 2 Hz, 1H, CH), 4.04 (t, 3J(H,H) = 8 Hz, 2H, CH2), 3.84 (s, 3H, CH3), 2.96 (t,

3J(H,H) = 8 Hz, 2H, CH2), 1.80-1.75 (m, 2H, CH2), 1.63-1.55 (m, 2H, CH2), 1.47-1.37

(m, 2H, CH2), 1.31-1.21 (m, 10H, CH2), 0.93 (t, 3J(H,H) = 7 Hz, 3H, CH3), 0.81 (t,

3J(H,H) = 7 Hz, 3H, CH3);

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3. Results – Publication Summaries

43

13C-NMR (CDCl3, 100 MHz, RT, ppm) δ = 146.6, 123.1, 120.9, 48.6, 35.2, 31.6, 30.0,

29.1, 28.9, 28.9, 26.4, 23.0, 22.5, 22.4, 14.0, 13.5;

IR (ATR, diamond crystal, neat): v = 894 (Re=O asymmetric);

Elemental analysis calcd. (%) for C16H31N2O4Re: C 38.31, H 6.23, N 5.58, O 12.76,

Re 37.12; found: C 38.43, H 6.71, N 5.64, Re 36.41.

1-Dodecyl-3-methylimidazolium perrhenate (27):

C16H31N2O4Re (501.64 g/mol); colorless powder; 95 % yield; m.p.: 49 °C;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 8.85 (s, 1 H, CH), 7.40 (m, 1 H, CH), 7.34

(m,1 H, CH), 4.21 (t, 3J(H,H) = 8 Hz, 2 H CH2), 4.01 (s, 3 H, CH3), 1.89 (t, 3J(H,H) =

8 Hz, 2 H CH2), 1.33–1.24 (m, 18 H CH2), 0.86 (t, 3J(H,H) = 8 Hz, 3 H, CH3);

13C NMR (CDCl3, 100 MHz, RT, ppm): δ = 136.4, 123.9, 122.4, 50.6, 36.7, 32.0,

30.3, 29.7, 29.7, 29.6, 29.5, 29,4, 29.1, 26.4, 22.8, 14.2;

IR (ATR, diamond crystal, neat): v = 900 (Re=O asymmetric);

Elemental analysis calcd. (%) for C16H31N2O4Re: C 38.31, H 6.23, N 5.58, O 12.76,

Re 37.12; found: C 38.52, H 6.31, N 5.57, Re 37.14.

1,2-Dimethyl-3-dodecylimidazolium perrhenate (28):

C17H33N2O4Re (515.66); colorless powder; 90 % yield; m.p.: 50 °C;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 7.31 (d, 3J(H,H) = 2 Hz, 1H, CH), 7.23 (d,

3J(H,H) = 2 Hz, 1H, CH), 4.06 (t, 3J(H,H) = 8 Hz, 2H, CH2), 3.84 (s, 3H, CH3), 2.64 (s,

3H, CH3), 1.79-1.70 (m, 2H, CH2), 1.30-1.20 (m, 18H, CH2), 0.84 (t, 3J(H,H) = 7 Hz,

3H, CH3);

13C-NMR (CDCl3, 100 MHz, RT, ppm) δ = 143.8, 122.8, 121.0, 48.9, 35.3, 31.9, 29.8,

29.6, 29.6, 29.4, 29.3, 29.1, 26.4, 22.7, 14.2, 9.5;

IR (ATR, diamond crystal, neat): v = 895 (Re=O asymmetric);

Elemental analysis calcd. (%) for C17H33N2O4Re: C 39.60, H 6.45, N 5.43, O 12.41,

Re 36.11; found: C 39.91, H 6.47, N 5.33, Re 36.44.

2-Butyl-1-dodecyl-3-methylimidazolium perrhenate (29):

C20H39N2O4Re (557.75 g/mol); off-white powder; 72 % yield; m.p.: 76 °C;

1H NMR (CDCl3, 400 MHz, RT, ppm): δ = 7.38 (d, 3J(H,H) = 2 Hz, 1H, CH), 7.28 (d,

3J(H,H) = 2 Hz, 1H, CH), 4.07 (t, 3J(H,H) = 8 Hz, 2H, CH2), 3.90 (s, 3H, CH3), 3.01 (t,

3J(H,H) = 8 Hz, 2H, CH2), 1.90-1.80 (m, 2H, CH2), 1.68-1.58 (m, 2H, CH2), 1.53-1.42

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3. Results – Publication Summaries

44

(m, 2H, CH2), 1.40-1.20 (m, 18H, CH2), 0.99 (t, 3J(H,H) = 7 Hz, 3H, CH3), 0.87 (t,

3J(H,H) = 7 Hz, 3H, CH3);

13C-NMR (CDCl3, 100 MHz, RT, ppm) δ = 146.9, 123.3, 121.0, 48.8, 35.4, 32.0, 30.2,

29.7,29.6, 29.5, 29.4, 29.2, 29.1, 26.6, 23.2, 22.6, 14.3, 13.7;

IR (ATR, diamond crystal, neat): v = 902 (Re=O asymmetric);

Elemental analysis calcd. (%) for C20H39N2O4Re: C 43.07, H 7.05, N 5.02, O 11.47,

Re 33.39; found: C 43.45, H 7.17, N 5.06, Re 32.57.

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4. Summary and Outlook

45

4 Summary and Outlook

The catalytic cycloaddition of CO2 with epoxides to cyclic carbonates is a sustainable

possibility for the utilization of this greenhouse gas as a chemical building block. Or-

ganocatalysts bear a great potential, because of the easy availability and handling,

as well as the lower price and toxicity compared to metal based systems. However,

efficient conversions for this reaction with metal-free catalysts are only possible by

applying high temperatures and pressures, as they are generally less active. Hence,

the major part of this thesis focuses on the development of tailored organocatalysts,

which allow milder reaction conditions and lead to a minimized carbon footprint of the

process. The long-term objective is thereby to achieve a comparable catalytic activity

to metal based systems in order to conduct cyclic carbonate synthesis at ambient

conditions with organocatalysts.

Although imidazolium halides are known metal-free catalysts for the synthesis of cy-

clic carbonates from CO2 and epoxides, the impact of the cation on the catalytic ac-

tivity was not understood in detail. Thus, imidazolium bromides with varying imidazo-

lium residues were synthesized and applied as catalysts for the synthesis of PC to

investigate the resulting effects on the reaction outcome. It was shown that the C2

proton at the imidazolium ring activates the epoxide by HB, which leads to facilitated

nucleophilic ring-opening and enhanced catalytic activity. This was corroborated by

FTIR studies of a mixture of catalyst and epoxide. Further, the formation of a free

carbene as a catalytic active species can be excluded as a C2 alkyl substituent only

slightly reduces the observed yields. On the basis of these results, the structure of

the imidazolium substitution pattern was tailored to reach higher catalytic activity. The

introduction of an electron-withdrawing wingtip results in higher acidity of the C2 pro-

ton and thus in a stronger HB donor capability and more pronounced activation of the

epoxide. In addition, the solubility of the catalyst in the reaction mixture was improved

by a long alkyl residue at the second wingtip position. Finally, the optimized catalyst

1-(2,3,4,5,6-pentafluorobenzyl)-3-octylimidazolium bromide (Figure 4.1) is able to

efficiently mediate the formation of a variety of cyclic carbonates under mild reaction

conditions (70 °C, 4 bar CO2, 16 h). Moreover, the catalyst can be easily recycled, it

remains constantly active for at least ten runs and no solvents or metals are required.

Consequently, an overall green approach for the cycloaddition of CO2 and epoxides

with minimized energy-input and carbon footprint was achieved.

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4. Summary and Outlook

46

Figure 4.1: Optimized imidazolium bromide catalyst structure for the cycloaddition of CO2 with epox-

ides.

In order to further increase the catalytic activity of imidazolium halide based catalysts,

the structural motif of the cation was modified. As aforementioned, the presence of

three hydroxy groups in spatial proximity leads to particularly effective organocata-

lysts because of the synergism deriving from the multiple HB donor groups. There-

fore, two imidazolium moieties were coupled with a hydroxy functionalized propylene

bridging unit. The resulting catalysts bear two acidic C2 protons and one hydroxy

group as three neighboring HB donor functionalities that are capable of interacting

during the cycloaddition reaction. DFT calculations have revealed that these three HB

donor groups activate the epoxide more efficiently and also stabilize intermediates,

so that an enhanced catalytic activity is achieved. To ensure high solubility in the re-

action mixture, the remaining second wingtips of the imidazolium cations were again

functionalized with n-octyl groups, leading to the optimized bisimidazolium bromide

catalyst (Figure 4.2). Compared to the previously described most active single imid-

azolium bromide, the reaction time could be reduced to 73 % by using the newly de-

veloped system under identical conditions. In addition, the catalyst is applicable with-

out solvents or metals for a broad scope of epoxides and reusable for a least ten re-

action runs without loss of activity. Consequently, the carbon footprint and sustaina-

bility of the reaction were successfully improved.

Figure 4.2: Bisimidazolium bromide catalyst bearing three neighboring HB donor groups.

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4. Summary and Outlook

47

The simple and versatile possibilities for the modification of imidazolium halides are

their main advantage for further investigations towards even more active organocata-

lysts. By introducing new structural motifs for an enhanced epoxide or CO2 activation,

high catalytic efficiency at ambient conditions could be reached. As a result, the activ-

ity gap between metal-based and metal-free systems could be minimized, leading to

more sustainable organocatalytic processes.

Binary mixtures consisting of niobium(V)chloride and nucleophiles like TBAB are

known to efficiently mediate the catalytic cycloaddition of CO2 and epoxides at room

temperature and under one atmosphere CO2 pressure. By using imidazolium bro-

mides as nucleophilic components instead of TBAB, alternative catalyst systems are

obtained, whereby the activity strongly depends on the imidazolium substituents. Un-

like imidazolium bromides as single catalysts, the presence of a C2 proton reduces

the activity. Due to the much stronger epoxide interaction of the Lewis acidic

(NbCl5)2, the HB activation by the cation is negligible. However, the degree of ion

pairing is higher when the imidazolium ring bears a C2 proton, which results in a low-

er anion nucleophilicity. Thus, imidazolium salts with alkyl substituents in C2 position

gave higher catalytic activities. Besides the ion pairing, the solubility of the imidazoli-

um bromides in the reaction mixture was determined as a crucial factor regarding the

activity. Therefore, imidazolium patterns based on aliphatic substituents generally

show better catalytic performance compared to aromatic wingtips. By tailoring the

imidazolium structure towards high solubility and small interionic attractions, a prom-

ising alternative to common TBAB as nucleophile was finally obtained (Figure 4.3).

However, the (NbCl5)2/nucleophile catalyst systems cannot be recycled without loss

of activity, which is a serious disadvantage. Future studies should hence focus on

suitable structural motifs for nucleophilic components that allow facile recycling pro-

cedures and constant catalytic activity for multiple runs at the same time. Conse-

quently, not only a cost-efficient binary catalyst with high catalytic activity, but also a

large sustainability could be realized.

Figure 4.3: Binary catalyst system by combination of (NbCl5)2 and imidazolium bromides.

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4. Summary and Outlook

48

As a metal-free alternative to the (NbCl5)2 binary catalyst systems, the polyol PETT

was used as an activation agent for epoxides in combination with nucleophiles. The

four hydroxy groups activate the epoxide by HB interactions, so that the nucleophilic

ring-opening is facilitated. It was shown that the cation structure of the nucleophile

has a major influence on the catalytic activity. This is particularly obvious if TBAI is

used instead of KI in combination with PETT, as the cyclic carbonate yield increases

by a factor of 16. The resulting PETT/TBAI system (Figure 4.4) is applicable for the

conversion of a variety of epoxides to their corresponding cyclic carbonates in high

yields at mild reaction conditions (70 C, 4 bar CO2, 16 h, 5 mol % catalysts). In con-

trast to other binary organocatalytic systems, the PETT/TBAI mixture is also easily

recyclable and can be reused without loss of activity for a minimum of eight consecu-

tive reaction runs. Additionally, no metals or solvents are needed and the compounds

are non-toxic, cost-efficient and readily available. Taking all these aspects into ac-

count, a highly sustainable catalyst system for the coupling of CO2 and epoxides with

low carbon footprint was achieved.

Figure 4.4: PETT/TBAI binary catalyst system for the cycloaddition of CO2 and epoxides.

However, more demanding reaction conditions for the PETT system have to be ap-

plied compared to the (NbCl5)2 binary mixtures, as efficient conversions at ambient

conditions are not yet possible. Nevertheless, the air and moisture stable metal-free

approach does not require elaborated inert gas techniques or water free reactants or

solvents. Therefore, time consuming preparations are redundant and safety problems

are avoided. This demonstrates the great potential of organocatalytic binary catalysts

as a sustainable approach. To minimize the carbon footprint of the process, new

structural motifs for more efficient epoxide activation should be the focus of further

investigations. As a result, high catalytic activity at ambient reaction conditions should

be the long-term goal regarding the cycloaddition of CO2 and epoxides by organocat-

alysts.

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4. Summary and Outlook

49

In the second part of this thesis, the biphasic epoxidation of olefins, with aqueous

H2O2 as sustainable oxidant, was investigated using imidazolium based catalyst sys-

tems.

For this purpose, carboxy-functionalized imidazolium salts were employed to form

catalytic active polyoxomolybdates in situ (Figure 4.5). Thus, additional organic acids

for lowering the pH value are redundant and the reaction procedure is simplified sig-

nificantly. Nevertheless, the catalytic activity depends on the acidity of the reaction

mixture and thereby on the ratio of imidazolium salt to metal precursor. The optimal

catalyst performance was determined with a tenfold excess of imidazolium salt, lead-

ing to good yields for the epoxidation of cis-cyclooctene (60 °C, 24 h, 1.5 eq. H2O2,

5.0 mol %). The presumably formed [MoxOy]2- clusters were determined as the cata-

lytic active species, as it was shown that oxygen transfer of potentially in situ gener-

ated peracids can be excluded. Moreover, the catalyst system could be recycled by

extraction and was reusable with negligible loss of activity for six reaction runs. Con-

clusively, simple and cost-efficient precursors were used to create a catalyst system

for the epoxidation of cis-cyclooctene with aqueous H2O2 in an environmentally be-

nign manner.

Figure 4.5: System for the in situ generation of catalytic active polyoxomolybdate species using a

carboxy-functionalized imidazolium salt.

To enhance the catalytic activity of this system, more comprehensive studies dealing

with the exact structure of the catalytic active species are needed. This would allow

the tailoring of the imidazolium substitution pattern towards the actual catalyst, lead-

ing to more efficient conversion rates for the epoxidation reaction. The scope of this

system should further be extended to show the applicability for other olefins than cis-

cyclooctene. Aside from molybdate precursors, other metal salts could also be used

to possibly generate even more active epoxidation catalysts in situ.

As an alternative system for the epoxidation of olefins with aqueous H2O2, imidazoli-

um perrhenates were used as catalysts for the first time. In contrast to earlier studies

regarding their equimolar application, it was demonstrated that also substoichiometric

amounts are capable of efficiently mediating the epoxidation reaction. To reveal the

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4. Summary and Outlook

50

impact of the cation on the activity, a database of imidazolium perrhenates with vary-

ing substitution patterns was synthesized and used as catalysts. As the reaction

mechanism is based on the activation of H2O2 by the [ReO4]- HB acceptor ability, the

shielding of the anion caused by interionic attractions has a major influence. There-

fore, alkyl substituents in C2 position of the imidazolium cation instead of a C2 proton

positively affect the reaction outcome, caused by the lower degree of ion pairing. This

results in a more reactive anion and hence more efficient H2O2 activation. The hydro-

phobicity of the catalysts is another fundamental factor for the activity of imidazolium

perrhenates in the biphasic epoxidation reaction of olefins with aqueous H2O2. For

suitable functionalization, it was found that HB interactions of the anion to H2O2 ena-

ble high solubility in the aqueous phase. This is not observed in the absence of the

oxidant or imidazolium cations with a too high hydrophobicity. However, it was shown

that proper modification of the solubility enables the imidazolium perrhenate to act as

a phase transfer catalyst, thereby transferring the olefin in the aqueous phase. This

assumes that the cation provides a catalyst hydrophobicity, which is not too low, so

that interaction with the olefin is possible. The optimized catalyst (Figure 4.6), regard-

ing ion pairing and solubility, catalyzes the formation of cyclooctene oxide in 88 %

yield (70 °C, 4 h, 2.5 eq. H2O2 (50 wt. %), 5.0 mol %). Additionally, the catalyst was

easily separated from the reaction mixture and exhibits high stability, as well as con-

stant catalytic activity for at least ten consecutive runs.

Figure 4.6: Optimized imidazolium perrhenate catalyst for olefin epoxidation with aqueous H2O2.

Also a variety of other olefins was converted efficiently, but with high selectivities for

the corresponding diols. The aim of future investigations could be to tailor the imidaz-

olium structure towards the desired substrate in order to reach higher selectivities for

the epoxide product. The introduction of functional groups at the cation moiety could

further lead to enhanced catalytic activity caused by more pronounced phase transfer

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4. Summary and Outlook

51

of the olefin or stronger H2O2 activation. Apart from the modification of the imidazoli-

um pattern, the substitution of [ReO4]- as HB acceptor for H2O2 activation bears a

vast potential. It is known from mechanistic investigations that the metal center does

not participate in the catalytic cycle, which proceeds via an outer-sphere mechanism.

This enables the possibility to exchange the expensive transition metal with metal-

free, much more cost-efficient and eco-friendly analogs like the omnipresent nitrate

[NO3]-, sulfate [SO4]

2-, phosphate [PO4]3- or acetate [OAc]- anions. Initial studies have

shown that such imidazolium salts are catalytically active for the epoxidation of cis-

cyclooctene. This paves the way to innovative, cost-efficient, readily available and

highly sustainable organocatalysts for the epoxidation of olefins with aqueous H2O2.

The future objective of this thesis is to develop a process, which enables direct cyclic

carbonate synthesis from olefins, CO2 and H2O2 or oxygen as eco-friendly oxidants.

For this purpose, the achieved results have to be combined to design a catalyst,

which is able to mediate both reactions consecutively at identical reaction conditions.

Another possibility could be the simultaneous application of two individual catalysts,

whereby the respective single compounds have to be compatible and do not disrupt

each other. When these challenges are solved, the synthesis of cyclic carbonates is

facilitated considerably and superior possibilities for more sustainable processes will

be provided.

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5. Bibliographic Data of Complete Publications

52

5 Bibliographic Data of Complete Publications

This chapter provides the reader with the bibliographic details of the publications

summarized in Chapter 3 of this thesis to facilitate the retrieval of the complete man-

uscripts and supporting information.

5.1 Cycloaddition of CO2 and Epoxides Catalyzed by Imidazolium Bro-

mides Under Mild Conditions: Influence of the Cation on Catalyst Activity

Michael H. Anthofer,‡a Michael E. Wilhelm,‡a Mirza Cokoja,*a Iulius I. E. Markovits,a

Alexander Pöthig,a János Mink,bc Wolfgang A. Herrmanna and Fritz E. Kühna

a Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universi-

tät München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany.

E-mail: [email protected]; Fax: +49 89 289 13473; Tel: +49 89 289 13478

b Hungarian Academy of Science, Chemical Research Center, Pusztszeri u. 59-67, 1025 Budapest,

Hungary

c Faculty of Information Technology, University of Pannonia, Egyetem u. 10, 8200 Veszprém, Hungary

‡ Equally contributing authors

Originally published in: Catal. Sci. Technol. 2014, 4, 1749 – 1758.

DOI: 10.1039/C3CY01024D

Hyperlink: http://pubs.rsc.org/en/Content/ArticleLanding/2014/CY/c3cy01024d#!divAbstract

5.2 Hydroxy-Functionalized Imidazolium Bromides as Catalysts for the

Cycloaddition of CO2 and Epoxides to Cyclic Carbonates

Michael H. Anthofer,‡a Michael E. Wilhelm,‡a Mirza Cokoja,*a Markus Drees,a

Wolfgang A. Herrmanna and Fritz E. Kühna

a Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universi-

tät München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany.

E-mail: [email protected]; Fax: +49 89 289 13473; Tel: +49 89 289 13478

‡ Equally contributing authors

Originally published in: ChemCatChem 2015, 7, 94 – 98.

DOI: 10.1002/cctc.201402754

Hyperlink: http://onlinelibrary.wiley.com/doi/10.1002/cctc.201402754/abstract

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5. Bibliographic Data of Complete Publications

53

5.3 Niobium(V)chloride and Imidazolium Bromides as Efficient Dual Cata-

lyst Systems for the Cycloaddition of Carbon Dioxide and Propylene Ox-

ide

Michael E. Wilhelm,‡a Michael H. Anthofer,‡a Robert M. Reich,a Valerio D’Elia,b

Jean-Marie Basset,b Wolfgang A. Herrmann,a Mirza Cokoja,*a and Fritz E. Kühn*a

a Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universi-

tät München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany.

E-mail: [email protected]; [email protected]

Fax: +49 89 289 13473; Tel: +49 89 289 13096

b KAUST Catalysis Center, King Abdullah University of Science and Technology, Thuwal, 23955

(Kingdom Saudi Arabia).

‡ Equally contributing authors

Originally published in: Catal. Sci. Technol. 2014, 4, 1638 – 1643.

DOI: 10.1039/C3CY01057K

Hyperlink: http://pubs.rsc.org/en/Content/ArticleLanding/2014/CY/c3cy01057k#!divAbstract

5.4 Cycloaddition of Carbon Dioxide and Epoxides Using Pentaerythritol

and Halides as Dual Catalyst System

Michael E. Wilhelm,‡a Michael H. Anthofer,‡a Mirza Cokoja,*a Iulius I. E. Markovits,a

Wolfgang A. Herrmanna and Fritz E. Kühna

a Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universi-

tät München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany.

E-mail: [email protected]; Fax: +49 89 289 13473; Tel: +49 89 289 13478

‡ Equally contributing authors

Originally published in: ChemSusChem 2014, 7, 1357 – 1360.

DOI: 10.1002/cssc.201301273

Hyperlink: http://onlinelibrary.wiley.com/doi/10.1002/cssc.201301273/abstract

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5. Bibliographic Data of Complete Publications

54

5.5 Epoxidations of Olefins Catalyzed by Polyoxomolybdates Formed in

situ in Ionic Liquids

Lilian R. Graser,a Sophie Jürgens,a Michael E. Wilhelm,a, Mirza Cokoja,a

Wolfgang A. Herrmanna and Fritz E. Kühn*a

a Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universi-

tät München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany.

E-mail: [email protected]; Fax: +49 89 289 13473; Tel: +49 89 289 13081

Originally published in: Z. Naturforsch. B 2013, 68b, 1138 – 1142.

DOI: 10.5560/ZNB.2013-3139

Hyperlink:

http://www.degruyter.com/dg/viewarticle/j$002fznb.2013.68.issue-10$002fznb.2013-

3139$002fznb.2013-3139.xml;jsessionid=6CE430BE69B6B32E52C03163EF5F2629

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6. Reprint Permissions

55

6 Reprint Permissions

6.1 RSC Publications

All manuscripts were reproduced by permission of The Royal Society of Chemistry.

The detailed bibliographic data and the corresponding hyperlinks of the respective

articles can be found in Chapter 5.

6.2 De Gruyter Publication

The manuscript published in the Zeitschrift für Naturforschung B was reproduced by

permission of De Gruyter. The detailed bibliographic data and the corresponding hy-

perlink of the respective article can be found in Chapter 5.

6.3 Wiley Publications

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6. Reprint Permissions

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Sons") consists of your license details and the terms and conditions provided by John Wiley and Sons and Copyright Clearance Center.

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Licensed Content Title Hydroxy-Functionalized Imidazolium Bromides as Catalysts for the Cycloaddition of CO2 and Epoxides to Cyclic Carbonates

Licensed Content Author Michael H. Anthofer,Michael E. Wilhelm,Mirza Cokoja,Markus Drees,Wolfgang A. Herrmann,Fritz E. Kühn

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Licensed Content Title Cycloaddition of Carbon Dioxide and Epoxides using Pentaerythritol and Halides as Dual Catalyst System

Licensed Content Author Michael E. Wilhelm,Michael H. Anthofer,Mirza Cokoja,Iulius I. E. Mar-kovits,Wolfgang A. Herrmann,Fritz E. Kühn

Licensed Content Date Mar 24, 2014

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Ionic Catalysts for the Cycloaddition of Carbon Dioxide with Epoxides and the Oxidation of Olefins

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7. References

62

7 References

[1] E. V. Kondratenko, G. Mul, J. Baltrusaitis, G. O. Larrazabal, J. Perez-Ramirez, Energy & Environmental Science 2013, 6, 3112-3135.

[2] W. V. o. t. C. I. ICAA, Technology Roadmaps on Energy & Climate Change 2013.

[3] a) C. R. A. G., van Santen, Catalysis for Renewables: From Feedstock to Energy Production, Wiley-VCH, 2007; b) D. M. Alonso, J. Q. Bond, J. A. Dumesic, Green Chemistry 2010, 12, 1493-1513.

[4] D. M. Alonso, S. G. Wettstein, J. A. Dumesic, Chemical Society Reviews 2012, 41, 8075-8098.

[5] J. K. Satyarthi, T. Chiranjeevi, D. T. Gokak, P. S. Viswanathan, Catalysis Science & Technology 2013, 3, 70-80.

[6] C. Maeda, Y. Miyazaki, T. Ema, Catalysis Science & Technology 2014, 4, 1482-1497.

[7] IEA, CO2 Emission from Fuel Combustion Highlights 2013. [8] M. Mikkelsen, M. Jorgensen, F. C. Krebs, Energy & Environmental Science

2010, 3, 43-81. [9] S. Suib, New and Future Developments in Catalysis Activation of Carbon

Dioxide, 2013. [10] M. Aresta, A. Dibenedetto, Dalton Transactions 2007, 0, 2975-2992. [11] G. Centi, E. A. Quadrelli, S. Perathoner, Energy & Environmental Science

2013, 6, 1711-1731. [12] M. North, R. Pasquale, C. Young, Green Chemistry 2010, 12, 1514-1539. [13] A. Decortes, A. M. Castilla, A. W. Kleij, Angewandte Chemie International

Edition 2010, 49, 9822-9837. [14] M. Aresta, A. Dibenedetto, A. Angelini, Chemical Reviews 2013, 114, 1709-

1742. [15] a) K. Xu, Chemical Reviews 2004, 104, 4303-4418; b) H. L. Parker, J.

Sherwood, A. J. Hunt, J. H. Clark, ACS Sustainable Chemistry & Engineering 2014, 2, 1739-1742.

[16] D. J. Darensbourg, W. Choi, O. Karroonnirun, N. Bhuvanesh, Macromolecules 2008, 41, 3493-3502.

[17] T. Tatsumi, Y. Watanabe, K. A. Koyano, Chemical Communications 1996, 2281-2282.

[18] J. H. Clements, Industrial & Engineering Chemistry Research 2003, 42, 663-674.

[19] L. Wang, L. Lin, G. Zhang, K. Kodama, M. Yasutake, T. Hirose, Chemical Communications 2014, 50, 14813-14816.

[20] R. Luo, X. Zhou, S. Chen, Y. Li, L. Zhou, H. Ji, Green Chemistry 2014, 16, 1496-1506.

[21] A. Sibaouih, P. Ryan, M. Leskelä, B. Rieger, T. Repo, Applied Catalysis A: General 2009, 365, 194-198.

[22] R. L. Paddock, S. T. Nguyen, Journal of the American Chemical Society 2001, 123, 11498-11499.

[23] A. Decortes, M. Martinez Belmonte, J. Benet-Buchholz, A. W. Kleij, Chemical Communications 2010, 46, 4580-4582.

[24] H. Xie, S. Li, S. Zhang, Journal of Molecular Catalysis A: Chemical 2006, 250, 30-34.

Page 75: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

7. References

63

[25] a) A. Monassier, V. D'Elia, M. Cokoja, H. Dong, J. D. A. Pelletier, J.-M. Basset, F. E. Kühn, ChemCatChem 2013, 5, 1321-1324; b) M. E. Wilhelm, M. H. Anthofer, R. M. Reich, V. D'Elia, J.-M. Basset, W. A. Herrmann, M. Cokoja, F. E. Kühn, Catalysis Science & Technology 2014, 4, 1638-1643.

[26] T. Yano, H. Matsui, T. Koike, H. Ishiguro, H. Fujihara, M. Yoshihara, T. Maeshima, Chemical Communications 1997, 1129-1130.

[27] a) D. W. C. MacMillan, Nature 2008, 455, 304-308; b) J. G. Hernandez, E. Juaristi, Chemical Communications 2012, 48, 5396-5409.

[28] a) B. L. M. Reetz, S. Jaroch, H. Weinmann, Organocatalysis, Springer-Verlag, 2008; b) P. MacLellan, Nat Chem 2013, 5, 896-897.

[29] a) H. G. A. Berkessel, Asymmetric Organocatalysis: From Biomimetic Concepts to Applications in Asymmetric Synthesis Wiley-VCH Verlag GmbH & Co. , 2005; b) E. N. Jacobsen, D. W. C. MacMillan, Proceedings of the National Academy of Sciences 2010, 107, 20618-20619.

[30] T. Nishikubo, A. Kameyama, J. Yamashita, M. Tomoi, W. Fukuda, Journal of Polymer Science Part A: Polymer Chemistry 1993, 31, 939-947.

[31] V. Calo, A. Nacci, A. Monopoli, A. Fanizzi, Organic Letters 2002, 4, 2561-2563.

[32] J.-Q. Wang, K. Dong, W.-G. Cheng, J. Sun, S.-J. Zhang, Catalysis Science & Technology 2012, 2, 1480-1484.

[33] J.-Q. Wang, D.-L. Kong, J.-Y. Chen, F. Cai, L.-N. He, Journal of Molecular Catalysis A: Chemical 2006, 249, 143-148.

[34] J. Sun, S. Zhang, W. Cheng, J. Ren, Tetrahedron Letters 2008, 49, 3588-3591.

[35] H. Büttner, K. Lau, A. Spannenberg, T. Werner, ChemCatChem 2015, 7, 459-467.

[36] a) Y. Zhou, S. Hu, X. Ma, S. Liang, T. Jiang, B. Han, Journal of Molecular Catalysis A: Chemical 2008, 284, 52-57; b) Y. Tsutsumi, K. Yamakawa, M. Yoshida, T. Ema, T. Sakai, Organic Letters 2010, 12, 5728-5731.

[37] A. J. R. Amaral, J. F. J. Coelho, A. C. Serra, Tetrahedron Letters 2013, 54, 5518-5522.

[38] a) J. Tharun, G. Mathai, R. Roshan, A. C. Kathalikkattil, K. Bomi, D.-W. Park, Physical Chemistry Chemical Physics 2013, 15, 9029-9033; b) K. R. Roshan, T. Jose, D. Kim, K. A. Cherian, D. W. Park, Catalysis Science & Technology 2014, 4, 963-970.

[39] a) Y. Du, F. Cai, D.-L. Kong, L.-N. He, Green Chemistry 2005, 7, 518-523; b) X. Chen, J. Sun, J. Wang, W. Cheng, Tetrahedron Letters 2012, 53, 2684-2688.

[40] Y. Du, J.-Q. Wang, J.-Y. Chen, F. Cai, J.-S. Tian, D.-L. Kong, L.-N. He, Tetrahedron Letters 2006, 47, 1271-1275.

[41] K. R. Roshan, T. Jose, A. C. Kathalikkattil, D. W. Kim, B. Kim, D. W. Park, Applied Catalysis A: General 2013, 467, 17-25.

[42] a) J. Tharun, Y. Hwang, R. Roshan, S. Ahn, A. C. Kathalikkattil, D.-W. Park, Catalysis Science & Technology 2012, 2, 1674-1680; b) Y. Zhao, J.-S. Tian, X.-H. Qi, Z.-N. Han, Y.-Y. Zhuang, L.-N. He, Journal of Molecular Catalysis A: Chemical 2007, 271, 284-289.

[43] D. Wei-Li, J. Bi, L. Sheng-Lian, L. Xu-Biao, T. Xin-Man, A. Chak-Tong, Journal of Molecular Catalysis A: Chemical 2013, 378, 326-332.

[44] a) W.-L. Wong, P.-H. Chan, Z.-Y. Zhou, K.-H. Lee, K.-C. Cheung, K.-Y. Wong, Chemsuschem 2008, 1, 67-70; b) W.-L. Wong, L. Y. S. Lee, K.-P. Ho, Z.-Y.

Page 76: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

7. References

64

Zhou, T. Fan, Z. Lin, K.-Y. Wong, Applied Catalysis A: General 2014, 472, 160-166.

[45] T. Yu, R. G. Weiss, Green Chemistry 2012, 14, 209-216. [46] Z.-Z. Yang, L.-N. He, C.-X. Miao, S. Chanfreau, Advanced Synthesis &

Catalysis 2010, 352, 2233-2240. [47] a) S. Foltran, J. Alsarraf, F. Robert, Y. Landais, E. Cloutet, H. Cramail, T.

Tassaing, Catalysis Science & Technology 2013, 3, 1046-1055; b) S. Foltran, R. Mereau, T. Tassaing, Catalysis Science & Technology 2014, 4, 1585-1597.

[48] D. Wei-Li, J. Bi, L. Sheng-Lian, L. Xu-Biao, T. Xin-Man, A. Chak-Tong, Applied Catalysis A: General 2014, 470, 183-188.

[49] T. Werner, H. Büttner, ChemSusChem 2014, 7, 3268-3271. [50] P. K. Khatri, S. L. Jain, K. T. Lim, Tetrahedron Letters 2013, 54, 6648-6650. [51] B. Chatelet, L. Joucla, J.-P. Dutasta, A. Martinez, K. C. Szeto, V. Dufaud,

Journal of the American Chemical Society 2013, 135, 5348-5351. [52] B. Chatelet, L. Joucla, J.-P. Dutasta, A. Martinez, V. Dufaud, Chemistry – A

European Journal 2014, 20, 8571-8574. [53] Y. Xiong, F. Bai, Z. Cui, N. Guo, R. Wang, Journal of Chemistry 2013, 2013, 9. [54] Y. P. Patil, P. J. Tambade, S. R. Jagtap, B. M. Bhanage, Journal of Molecular

Catalysis A: Chemical 2008, 289, 14-21. [55] a) Y. Xiong, H. Wang, R. Wang, Y. Yan, B. Zheng, Y. Wang, Chemical

Communications 2010, 46, 3399-3401; b) Y. Xiong, Y. Wang, H. Wang, R. Wang, Polymer Chemistry 2011, 2, 2306-2315.

[56] T. Sakai, Y. Tsutsumi, T. Ema, Green Chemistry 2008, 10, 337-341. [57] T. Takahashi, T. Watahiki, S. Kitazume, H. Yasuda, T. Sakakura, Chemical

Communications 2006, 0, 1664-1666. [58] Q.-W. Song, L.-N. He, J.-Q. Wang, H. Yasuda, T. Sakakura, Green Chemistry

2013, 15, 110-115. [59] a) J. D. Holbrey, R. D. Rogers, R. A. Mantz, P. C. Trulove, V. A. Cocalia, A. E.

Visser, J. L. Anderson, J. L. Anthony, J. F. Brennecke, E. J. Maginn, T. Welton, R. A. Mantz, in Ionic Liquids in Synthesis, Wiley-VCH Verlag GmbH & Co. KGaA, 2008, pp. 57-174; b) T. Peppel, C. Roth, K. Fumino, D. Paschek, M. Köckerling, R. Ludwig, Angewandte Chemie International Edition 2011, 50, 6661-6665.

[60] M. G. Freire, L. M. N. B. F. Santos, A. M. Fernandes, J. A. P. Coutinho, I. M. Marrucho, Fluid Phase Equilibria 2007, 261, 449-454.

[61] A. Wulf, K. Fumino, R. Ludwig, Angewandte Chemie International Edition 2010, 49, 449-453.

[62] J. Peng, Y. Deng, New Journal of Chemistry 2001, 25, 639-641. [63] H. Kawanami, A. Sasaki, K. Matsui, Y. Ikushima, Chemical Communications

2003, 896-897. [64] D.-W. Park, N.-Y. Mun, K.-H. Kim, I. Kim, S.-W. Park, Catalysis Today 2006,

115, 130-133. [65] J.-Q. Wang, W.-G. Cheng, J. Sun, T.-Y. Shi, X.-P. Zhang, S.-J. Zhang, RSC

Advances 2014, 4, 2360-2367. [66] L. Han, H.-J. Choi, S.-J. Choi, B. Liu, D.-W. Park, Green Chemistry 2011, 13,

1023-1028. [67] a) L. Han, S.-J. Choi, M.-S. Park, S.-M. Lee, Y.-J. Kim, M.-I. Kim, B. Liu, D.-W.

Park, Reac Kinet Mech Cat 2012, 106, 25-35; b) J. Sun, L. Han, W. Cheng, J. Wang, X. Zhang, S. Zhang, ChemSusChem 2011, 4, 502-507.

[68] L.-F. Xiao, D.-W. Lv, D. Su, W. Wu, H.-F. Li, Journal of Cleaner Production 2014, 67, 285-290.

Page 77: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

7. References

65

[69] H. Sun, D. Zhang, The Journal of Physical Chemistry A 2007, 111, 8036-8043. [70] M. H. Anthofer, M. E. Wilhelm, M. Cokoja, I. I. E. Markovits, A. Pöthig, J. Mink,

W. A. Herrmann, F. E. Kühn, Catalysis Science & Technology 2014, 4, 1749-1758.

[71] A.-L. Girard, N. Simon, M. Zanatta, S. Marmitt, P. Goncalves, J. Dupont, Green Chemistry 2014, 16, 2815-2825.

[72] M. H. Anthofer, M. E. Wilhelm, M. Cokoja, M. Drees, W. A. Herrmann, F. E. Kühn, ChemCatChem 2015, 7, 94-98.

[73] C. J. Whiteoak, A. Nova, F. Maseras, A. W. Kleij, ChemSusChem 2012, 5, 2032-2038.

[74] Y. Xie, Z. Zhang, T. Jiang, J. He, B. Han, T. Wu, K. Ding, Angewandte Chemie International Edition 2007, 46, 7255-7258.

[75] H.-J. Choi, M. Selvaraj, D.-W. Park, Chemical Engineering Science 2013. [76] L. Han, H. Li, S.-J. Choi, M.-S. Park, S.-M. Lee, Y.-J. Kim, D.-W. Park, Applied

Catalysis A: General 2012, 429–430, 67-72. [77] Z.-Z. Yang, Y. Zhao, G. Ji, H. Zhang, B. Yu, X. Gao, Z. Liu, Green Chemistry

2014, 16, 3724-3728. [78] a) J. Sun, W. Cheng, W. Fan, Y. Wang, Z. Meng, S. Zhang, Catalysis Today

2009, 148, 361-367; b) T.-Y. Shi, J.-Q. Wang, J. Sun, M.-H. Wang, W.-G. Cheng, S.-J. Zhang, RSC Advances 2013, 3, 3726-3732.

[79] R. A. Watile, K. M. Deshmukh, K. P. Dhake, B. M. Bhanage, Catalysis Science & Technology 2012, 2, 1051-1055.

[80] a) J.-Q. Wang, X.-D. Yue, F. Cai, L.-N. He, Catalysis Communications 2007, 8, 167-172; b) L. Han, S.-W. Park, D.-W. Park, Energy & Environmental Science 2009, 2, 1286-1292; c) S. Udayakumar, V. Raman, H.-L. Shim, D.-W. Park, Applied Catalysis A: General 2009, 368, 97-104; d) J. N. Appaturi, F. Adam, Applied Catalysis B: Environmental 2013, 136–137, 150-159; e) C. Aprile, F. Giacalone, P. Agrigento, L. F. Liotta, J. A. Martens, P. P. Pescarmona, M. Gruttadauria, ChemSusChem 2011, 4, 1830-1837.

[81] J. Wang, J. Leong, Y. Zhang, Green Chemistry 2014, 16, 4515-4519. [82] K. R. Roshan, G. Mathai, J. Kim, J. Tharun, G.-A. Park, D.-W. Park, Green

Chemistry 2012, 14, 2933-2940. [83] J. Sun, J. Wang, W. Cheng, J. Zhang, X. Li, S. Zhang, Y. She, Green

Chemistry 2012, 14, 654-660. [84] C. J. Whiteoak, A. H. Henseler, C. Ayats, A. W. Kleij, M. A. Pericas, Green

Chemistry 2014, 16, 1552-1559. [85] a) K. R. Roshan, A. C. Kathalikkattil, J. Tharun, D. W. Kim, Y. S. Won, D. W.

Park, Dalton Transactions 2014, 43, 2023-2031; b) Z. Yang, J. Sun, W. Cheng, J. Wang, Q. Li, S. Zhang, Catalysis Communications 2014, 44, 6-9.

[86] a) J. Sun, W. Cheng, Z. Yang, J. Wang, T. Xu, J. Xin, S. Zhang, Green Chemistry 2014, 16, 3071-3078; b) S. Liang, H. Liu, T. Jiang, J. Song, G. Yang, B. Han, Chemical Communications 2011, 47, 2131-2133.

[87] Z. Wu, H. Xie, X. Yu, E. Liu, ChemCatChem 2013, 5, 1328-1333. [88] J. Song, Z. Zhang, B. Han, S. Hu, W. Li, Y. Xie, Green Chemistry 2008, 10,

1337-1341. [89] J.-W. Huang, M. Shi, The Journal of Organic Chemistry 2003, 68, 6705-6709. [90] Y.-M. Shen, W.-L. Duan, M. Shi, Advanced Synthesis & Catalysis 2003, 345,

337-340. [91] J.-Q. Wang, J. Sun, W.-G. Cheng, K. Dong, X.-P. Zhang, S.-J. Zhang,

Physical Chemistry Chemical Physics 2012, 14, 11021-11026.

Page 78: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

7. References

66

[92] M. E. Wilhelm, M. H. Anthofer, M. Cokoja, I. I. E. Markovits, W. A. Herrmann, F. E. Kühn, ChemSusChem 2014, 7, 1357-1360.

[93] A. M. Hardman-Baldwin, A. E. Mattson, ChemSusChem 2014, 7, 3275-3278. [94] a) K. Sato, M. Aoki, M. Ogawa, T. Hashimoto, R. Noyori, The Journal of

Organic Chemistry 1996, 61, 8310-8311; b) N. Mizuno, K. Yamaguchi, K. Kamata, Coordination Chemistry Reviews 2005, 249, 1944-1956; c) K. Kamata, M. Kotani, K. Yamaguchi, S. Hikichi, N. Mizuno, Chemistry – A European Journal 2007, 13, 639-648.

[95] S. A. Hauser, M. Cokoja, F. E. Kühn, Catalysis Science & Technology 2013, 3, 552-561.

[96] S. T. Oyama, in Mechanisms in Homogeneous and Heterogeneous Epoxidation Catalysis (Ed.: S. T. Oyama), Elsevier, Amsterdam, 2008, pp. 3-99.

[97] M. R. Consulting, World Propylene Oxide (PO) Market to See Sustained Growth in Years Ahead 2014.

[98] P. Bassler, H.-G. Göbbel-, M. Weidenbach, Chemical Engineering Transactions 2010, 21, 571-576.

[99] T. A. Nijhuis, M. Makkee, J. A. Moulijn, B. M. Weckhuysen, Industrial & Engineering Chemistry Research 2006, 45, 3447-3459.

[100] V. Russo, R. Tesser, E. Santacesaria, M. Di Serio, Industrial & Engineering Chemistry Research 2013, 52, 1168-1178.

[101] L. Sumitomo Chemical Co., J. Tsuji, J. Yamamoto, M. Ishino, N. Oku, Development of New Propylene Oxide Process 2006.

[102] R. A. Sheldon, Chemical Communications 2008, 3352-3365. [103] S. B. Shin, D. Chadwick, Industrial & Engineering Chemistry Research 2010,

49, 8125-8134. [104] B. S. Lane, K. Burgess, Chemical Reviews 2003, 103, 2457-2474. [105] a) S. Huber, M. Cokoja, F. E. Kühn, Journal of Organometallic Chemistry

2014, 751, 25-32; b) Q. H. Xia, H. Q. Ge, C. P. Ye, Z. M. Liu, K. X. Su, Chemical Reviews 2005, 105, 1603-1662.

[106] D. J. Cole-Hamilton, Science 2003, 299, 1702-1706. [107] a) M. J. Muldoon, Dalton Transactions 2010, 39, 337-348; b) W. Keim, Green

Chemistry 2003, 5, 105-111; c) B. Cornils, W. A. Herrmann, I. T. Horváth, W. Leitner, S. Mecking, H. Olivier-Bourbigou, D. Vogt, in Multiphase Homogeneous Catalysis, Wiley-VCH Verlag GmbH, 2008.

[108] C. M. Gordon, Applied Catalysis A: General 2001, 222, 101-117. [109] Q. Zhang, S. Zhang, Y. Deng, Green Chemistry 2011, 13, 2619-2637. [110] J. Muzart, Advanced Synthesis & Catalysis 2006, 348, 275-295. [111] R. D. Rogers, K. R. Seddon, Science 2003, 302, 792-793. [112] J. P. Hallett, T. Welton, Chemical Reviews 2011, 111, 3508-3576. [113] C. E. Song, E. J. Roh, Chemical Communications 2000, 837-838. [114] K. A. Srinivas, A. Kumar, S. M. S. Chauhan, Chemical Communications 2002,

2456-2457. [115] a) D. Betz, A. Raith, M. Cokoja, F. E. Kühn, ChemSusChem 2010, 3, 559-562;

b) M. Herbert, A. Galindo, F. Montilla, Catalysis Communications 2007, 8, 987-990.

[116] D. Betz, W. A. Herrmann, F. E. Kühn, Journal of Organometallic Chemistry 2009, 694, 3320-3324.

[117] a) F. E. Kühn, J. Zhao, M. Abrantes, W. Sun, C. A. M. Afonso, L. C. Branco, I. S. Gonçalves, M. Pillinger, C. C. Romão, Tetrahedron Letters 2005, 46, 47-52;

Page 79: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

7. References

67

b) J. Dupont, J. Spencer, Angewandte Chemie International Edition 2004, 43, 5296-5297.

[118] M. Mąkosza, M. Fedoryński, Catalysis Reviews 2003, 45, 321-367. [119] M. Halpern, in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH

Verlag GmbH & Co. KGaA, 2000. [120] E. V. Dehmlow, M. Slopianka, Chemische Berichte 1979, 112, 2765-2768. [121] I. V. Kozhevnikov, Chemical Reviews 1998, 98, 171-198. [122] S.-S. Wang, G.-Y. Yang, Chemical Reviews 2015. [123] R. Noyori, M. Aoki, K. Sato, Chemical Communications 2003, 1977-1986. [124] X. Zuwei, Z. Ning, S. Yu, L. Kunlan, Science 2001, 292, 1139-1141. [125] K. Kamata, K. Yonehara, Y. Sumida, K. Yamaguchi, S. Hikichi, N. Mizuno,

Science 2003, 300, 964-966. [126] a) A. Kumar, Catalysis Communications 2007, 8, 913-916; b) L. Liu, C. Chen,

X. Hu, T. Mohamood, W. Ma, J. Lin, J. Zhao, New Journal of Chemistry 2008, 32, 283-289.

[127] L. Hua, Y. Qiao, Y. Yu, W. Zhu, T. Cao, Y. Shi, H. Li, B. Feng, Z. Hou, New Journal of Chemistry 2011, 35, 1836-1841.

[128] Y. Qiao, Z. Hou, H. Li, Y. Hu, B. Feng, X. Wang, L. Hua, Q. Huang, Green Chemistry 2009, 11, 1955-1960.

[129] H. Li, Z. Hou, Y. Qiao, B. Feng, Y. Hu, X. Wang, X. Zhao, Catalysis Communications 2010, 11, 470-475.

[130] J. Chen, L. Hua, W. Zhu, R. Zhang, L. Guo, C. Chen, H. Gan, B. Song, Z. Hou, Catalysis Communications 2014, 47, 18-21.

[131] Y. Leng, J. Wang, D. Zhu, M. Zhang, P. Zhao, Z. Long, J. Huang, Green Chemistry 2011, 13, 1636-1639.

[132] K. Yamaguchi, C. Yoshida, S. Uchida, N. Mizuno, Journal of the American Chemical Society 2005, 127, 530-531.

[133] a) A. Pourjavadi, S. H. Hosseini, F. Matloubi Moghaddam, B. Koushki Foroushani, C. Bennett, Green Chemistry 2013, 15, 2913-2919; b) Y. Leng, W. Zhang, J. Wang, P. Jiang, Applied Catalysis A: General 2012, 445–446, 306-311.

[134] M.-D. Zhou, M.-J. Liu, L.-L. Huang, J. Zhang, J.-Y. Wang, X.-B. Li, F. E. Kühn, S.-L. Zang, Green Chemistry 2015, 17, 1186-1193.

[135] R. Graser Lilian, S. Jürgens, E. Wilhelm Michael, M. Cokoja, A. Herrmann Wolfgang, E. Kühn Fritz, in Zeitschrift für Naturforschung B, Vol. 68, 2013, p. 1138.

[136] K. Neimann, R. Neumann, Organic Letters 2000, 2, 2861-2863. [137] M. C. A. van Vliet, I. W. C. E. Arends, R. A. Sheldon, Synlett 2001, 2001,

0248-0250. [138] S. P. de Visser, J. Kaneti, R. Neumann, S. Shaik, The Journal of Organic

Chemistry 2003, 68, 2903-2912. [139] A. Berkessel, J. A. Adrio, Advanced Synthesis & Catalysis 2004, 346, 275-

280. [140] A. Berkessel, J. A. Adrio, D. Hüttenhain, J. M. Neudörfl, Journal of the

American Chemical Society 2006, 128, 8421-8426. [141] A. Berkessel, J. A. Adrio, Journal of the American Chemical Society 2006,

128, 13412-13420. [142] A. Berkessel, J. Krämer, F. Mummy, J.-M. Neudörfl, R. Haag, Angewandte

Chemie International Edition 2013, 52, 739-743. [143] B. Zhang, M.-D. Zhou, M. Cokoja, J. Mink, S.-L. Zang, F. E. Kühn, RSC

Advances 2012, 2, 8416-8420.

Page 80: Ionic Catalysts for the Cycloaddition of Carbon Dioxide with … · 2015-08-20 · with Epoxides and the Oxidation of Olefins Michael Edmund Wilhelm Vollständiger Abdruck der von

7. References

68

[144] I. I. E. Markovits, W. A. Eger, S. Yue, M. Cokoja, C. J. Münchmeyer, B. Zhang, M.-D. Zhou, A. Genest, J. Mink, S.-L. Zang, N. Rösch, F. E. Kühn, Chemistry – A European Journal 2013, 19, 5972-5979.

[145] F. E. Kühn, A. M. Santos, I. S. Gonçalves, C. C. Romão, A. D. Lopes, Applied Organometallic Chemistry 2001, 15, 43-50.

[146] a) F. Gu, H. Dong, Y. Li, Z. Si, F. Yan, Macromolecules 2014, 47, 208-216; b) H. Tian, Z. Yu, A. Hagfeldt, L. Kloo, L. Sun, Journal of the American Chemical Society 2011, 133, 9413-9422; c) I. Arellano, J. Guarino, F. Paredes, S. Arco, J Therm Anal Calorim 2011, 103, 725-730; d) A. Aupoix, B. Pégot, G. Vo-Thanh, Tetrahedron 2010, 66, 1352-1356; e) I. Dinares, C. Garcia de Miguel, A. Ibanez, N. Mesquida, E. Alcalde, Green Chemistry 2009, 11, 1507-1510; f) A. Fürstner, M. Alcarazo, R. Goddard, C. W. Lehmann, Angewandte Chemie International Edition 2008, 47, 3210-3214; g) P. Lucas, N. E. Mehdi, H. A. Ho, D. Bélanger, L. Breau, Synthesis 2000, 2000, 1253-1258.

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8. Curriculum Vitae and Publications

69

8 Curriculum Vitae and Publications

8.1 Curriculum Vitae

PhD/Education

07/2012 – 07/2015 PhD in Chemistry

Technical University Munich (TUM)

Catalysis Research Center (CRC)

Supervisor: Prof. Dr. Dr. h.c. mult. W.A. Herrmann

“Ionic Catalysts for the Cycloaddition of Carbon Dioxide with Epox-

ides and the Oxidation of Olefins“

Design, synthesis & characterization of novel catalysts

Investigation of catalytic properties & mechanisms

Optimization of reaction & catalysis parameters

Preparation of 12 publications & presentations

Supervision and education of students

Assistant for beginners and advanced students

10/2009 – 04/2012 Master of Science Chemistry

Technical University Munich (TUM)

Major subject: Organic chemistry

Minor subject: Chemistry of macromolecules, colloids, interfaces

Master’s-Thesis: “Copolymerization of CO2 with Reactive Monomers“

10/2006 – 09/2009 Bachelor of Science Chemistry

Technical University Munich (TUM)

Bachelor‘s-Thesis: “ Sorption and Transport of Hydrocarbons in

HZSM 5 Studied by Infrared Spectroscopy“

09/1996 – 06/2006 Allgemeine Hochschulreife

Allgäu-Gymnasium, Kempten

Surname Wilhelm

First name Michael

Date of Birth October 25th 1985

Place of Birth Memmingen, Germany

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8.2 Journal and Book Contributions

1) “Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide by

Using Organocatalysts”

M. Cokoja, M. E. Wilhelm*, M. H. Anthofer*, W. A. Herrmann, Fritz E.

Kühn, ChemSusChem 2015, 7, 2436 – 2454.

2) “Hydroxy-Functionalized Imidazolium Bromides as Catalysts for the

Cycloaddition of CO2 and Epoxides to Cyclic Carbonates”

M. H. Anthofer*, M. E. Wilhelm*, M. Cokoja, M. Drees, W. A.

Herrmann, Fritz E. Kühn, ChemCatChem 2015, 7, 94 – 98.

3) “Cycloaddition of Carbon Dioxide and Epoxides Using Pentaerythritol

and Halides as Dual Catalyst System”

M. E. Wilhelm*, M. H. Anthofer*, M. Cokoja, I. I. E. Markovits, W. A.

Herrmann, F. E. Kühn, ChemSusChem 2014, 7, 1357 – 1360.

4) “Cycloaddition of CO2 and Epoxides Catalyzed by Imidazolium Bro-

mides at Mild Conditions: Influence of the Cation on Catalyst Activity”

M. H. Anthofer*, M. E. Wilhelm*, M. Cokoja, I. I. E. Markovits, A.

Pöthig, J. Mink, W. A. Herrmann, F. E. Kühn, Catal. Sci. Technol.

2014, 4, 1749 – 1758.

5) “Niobium(V)chloride and Imidazolium Bromides as Efficient Dual Cata-

lyst System for the Cycloaddition of Carbon Dioxide and Propylene

Oxide”

M. E. Wilhelm*, M. H. Anthofer*, R. M. Reich, V. D’Elia, J.-M. Basset,

W. A. Herrmann, M. Cokoja, F. E. Kühn, Catal. Sci. Technol. 2014, 4,

1638 – 1643.

6) ”Valorization of Carbon Dioxide to Organic Products with Organocata-

lysts”

M. H. Anthofer*, M. E. Wilhelm*, M. Cokoja, F. E. Kühn, in Transfor-

mation and Utilization of Carbon Dioxide (Eds.: B.M. Bhanage, M.

Arai), Springer Berlin Heidelberg, 2014, 3 – 37.

7) “Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in-

situ in Ionic Liquids”

L. R. Graser, S. Jürgens, M. E. Wilhelm, M. Cokoja, W. A. Herrmann,

F. E. Kühn, Zeitschrift für Naturforschung B 2013, 68, 1138 – 1142.

* equally contributing authors

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8.3 Talk and Poster Presentations

03/2015 Poster 48. Jahrestreffen Deutscher Katalytiker, Weimar

”Tailor-Made Dual Catalyst Systems for the Cycloaddition of CO2 to

Epoxides”

03/2015 Poster, 48. Jahrestreffen Deutscher Katalytiker, Weimar

”Perrhenathaltige ionische Flüssigkeiten als Katalysatoren in der Ole-

finepoxidierung: Löslichkeit, Stabilität und Kinetik“

10/2014 Poster, 7th Green Solvents Conference, Dresden

”Tandem Catalyst Systems for the Chemical Fixation of CO2 with

Epoxides to Cyclic Carbonates“

08/2014 Talk, 248th ACS National Meeting & Exposition, San Francisco

“Imidazolium and Dual Catalyst Systems for the Fixation of CO2 as

Cyclic Carbonates”

06/2013 Poster, 7th Forum of Molecular Catalysis, Heidelberg

“Recyclable Organocatalytic System for the Chemical Fixation of CO2

at Mild Reaction Conditions”